/*****************************************************************************

Copyright (c) 1997, 2017, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2015, 2023, MariaDB Corporation.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA

*****************************************************************************/

/***************************************************//**
@file row/row0sel.cc
Select

Created 12/19/1997 Heikki Tuuri
*******************************************************/

#define MYSQL_SERVER
#include "row0sel.h"
#include "dict0dict.h"
#include "dict0boot.h"
#include "trx0undo.h"
#include "trx0trx.h"
#include "trx0purge.h"
#include "trx0rec.h"
#include "btr0btr.h"
#include "btr0cur.h"
#include "btr0sea.h"
#include "gis0rtree.h"
#include "mach0data.h"
#include "que0que.h"
#include "row0upd.h"
#include "row0row.h"
#include "row0vers.h"
#include "rem0cmp.h"
#include "lock0lock.h"
#include "eval0eval.h"
#include "pars0sym.h"
#include "pars0pars.h"
#include "row0mysql.h"
#include "buf0lru.h"
#include "srv0srv.h"
#include "srv0mon.h"
#include "sql_error.h"
#include "sql_class.h" // THD
#ifdef WITH_WSREP
#include "mysql/service_wsrep.h" /* For wsrep_thd_skip_locking */
#endif

/* Maximum number of rows to prefetch; MySQL interface has another parameter */
#define SEL_MAX_N_PREFETCH	16

/* Number of rows fetched, after which to start prefetching; MySQL interface
has another parameter */
#define SEL_PREFETCH_LIMIT	1

/* When a select has accessed about this many pages, it returns control back
to que_run_threads: this is to allow canceling runaway queries */

#define SEL_COST_LIMIT	100

/* Flags for search shortcut */
#define SEL_FOUND	0
#define	SEL_EXHAUSTED	1
#define SEL_RETRY	2

/********************************************************************//**
Returns TRUE if the user-defined column in a secondary index record
is alphabetically the same as the corresponding BLOB column in the clustered
index record.
NOTE: the comparison is NOT done as a binary comparison, but character
fields are compared with collation!
@return whether the columns are equal */
static
bool
row_sel_sec_rec_is_for_blob(
/*========================*/
	ulint		mtype,		/*!< in: main type */
	ulint		prtype,		/*!< in: precise type */
	ulint		mbminlen,	/*!< in: minimum length of
					a character, in bytes */
	ulint		mbmaxlen,	/*!< in: maximum length of
					a character, in bytes */
	const byte*	clust_field,	/*!< in: the locally stored part of
					the clustered index column, including
					the BLOB pointer; the clustered
					index record must be covered by
					a lock or a page latch to protect it
					against deletion (rollback or purge) */
	ulint		clust_len,	/*!< in: length of clust_field */
	const byte*	sec_field,	/*!< in: column in secondary index */
	ulint		sec_len,	/*!< in: length of sec_field */
	ulint		prefix_len,	/*!< in: index column prefix length
					in bytes, or 0 for full column */
	dict_table_t*	table)		/*!< in: table */
{
	ulint	len;
	byte	buf[REC_VERSION_56_MAX_INDEX_COL_LEN + 1];

	/* This function should never be invoked on tables in
	ROW_FORMAT=REDUNDANT or ROW_FORMAT=COMPACT, because they
	should always contain enough prefix in the clustered index record. */
	ut_ad(dict_table_has_atomic_blobs(table));
	ut_a(clust_len >= BTR_EXTERN_FIELD_REF_SIZE);
	ut_ad(!prefix_len || prefix_len >= sec_len);
	ut_a(prefix_len <= sizeof buf);

	if (!memcmp(clust_field + clust_len - BTR_EXTERN_FIELD_REF_SIZE,
		    field_ref_zero, BTR_EXTERN_FIELD_REF_SIZE)) {
		/* The externally stored field was not written yet.
		This record should only be seen by
		trx_rollback_recovered() or any
		TRX_ISO_READ_UNCOMMITTED transactions. */
		return false;
	}

	len = btr_copy_externally_stored_field_prefix(
		buf, prefix_len ? prefix_len : sizeof buf,
		table->space->zip_size(),
		clust_field, clust_len);

	if (len == 0) {
		/* The BLOB was being deleted as the server crashed.
		There should not be any secondary index records
		referring to this clustered index record, because
		btr_free_externally_stored_field() is called after all
		secondary index entries of the row have been purged. */
		return false;
	}

	if (prefix_len) {
		len = dtype_get_at_most_n_mbchars(prtype, mbminlen, mbmaxlen,
						  prefix_len, len,
						  reinterpret_cast<const char*>
						  (buf));
	} else if (len >= sizeof buf) {
		ut_ad("too long column" == 0);
		return false;
	}

	return !cmp_data(mtype, prtype, false, buf, len, sec_field, sec_len);
}

/** Function to read the secondary spatial index, calculate
the minimum bounding rectangle for clustered index record
and secondary index record and compare it.
@param sec_rec		secondary index record
@param sec_index	spatial secondary index
@param clust_rec	clustered index record
@param clust_index	clustered index
@retval DB_SUCCESS_LOCKED_REC if the secondary record is equal to the
	corresponding fields in the clustered record, when compared with
	collation;
@retval DB_SUCCESS if not equal */
static
dberr_t
row_sel_spatial_sec_rec_is_for_clust_rec(
  const rec_t *sec_rec, const dict_index_t *sec_index,
  const rec_t *clust_rec, dict_index_t *clust_index)
{
  mem_heap_t *heap= mem_heap_create(256);
  rec_offs clust_offsets_[REC_OFFS_NORMAL_SIZE];
  rec_offs *clust_offs= clust_offsets_;
  ulint clust_len;

  rec_offs_init(clust_offsets_);
  ulint clust_pos= dict_col_get_clust_pos(
    dict_index_get_nth_col(sec_index, 0), clust_index);
  clust_offs= rec_get_offsets(clust_rec, clust_index, clust_offs,
                              clust_index->n_core_fields, clust_pos + 1,
                              &heap);
  ut_ad(sec_index->n_user_defined_cols == 1);
  const byte *clust_field= rec_get_nth_field(clust_rec, clust_offs,
                                             clust_pos, &clust_len);
  if (clust_len == UNIV_SQL_NULL || clust_len < GEO_DATA_HEADER_SIZE)
  {
    ut_ad("corrupted geometry column" == 0);
err_exit:
    mem_heap_free(heap);
    return DB_SUCCESS;
  }

  /* For externally stored field, we need to get full
  geo data to generate the MBR for comparing. */
  if (rec_offs_nth_extern(clust_offs, clust_pos))
  {
    clust_field= btr_copy_externally_stored_field(
      &clust_len, clust_field, sec_index->table->space->zip_size(),
      clust_len, heap);
    if (clust_field == NULL)
    {
      ut_ad("corrupted geometry blob" == 0);
      goto err_exit;
    }
  }

  ut_ad(clust_len >= GEO_DATA_HEADER_SIZE);
  rtr_mbr_t tmp_mbr;
  rtr_mbr_t sec_mbr;

  rtree_mbr_from_wkb(
    clust_field + GEO_DATA_HEADER_SIZE,
    static_cast<uint>(clust_len - GEO_DATA_HEADER_SIZE),
    SPDIMS, reinterpret_cast<double*>(&tmp_mbr));

  rtr_read_mbr(sec_rec, &sec_mbr);

  mem_heap_free(heap);
  return MBR_EQUAL_CMP(&sec_mbr, &tmp_mbr)
         ? DB_SUCCESS_LOCKED_REC
         : DB_SUCCESS;
}

/** Returns TRUE if the user-defined column values in a secondary index record
are alphabetically the same as the corresponding columns in the clustered
index record.
NOTE: the comparison is NOT done as a binary comparison, but character
fields are compared with collation!
@param[in]	sec_rec		secondary index record
@param[in]	sec_index	secondary index
@param[in]	clust_rec	clustered index record;
				must be protected by a page s-latch
@param[in]	clust_index	clustered index
@param[in]	thr		query thread
@retval	DB_COMPUTE_VALUE_FAILED in case of virtual column value computation
	failure.
@retval DB_SUCCESS_LOCKED_REC if the secondary record is equal to the
	corresponding fields in the clustered record, when compared with
	collation;
@retval DB_SUCCESS if not equal or if the clustered record has been marked
	for deletion */
static
dberr_t
row_sel_sec_rec_is_for_clust_rec(
	const rec_t*	sec_rec,
	dict_index_t*	sec_index,
	const rec_t*	clust_rec,
	dict_index_t*	clust_index,
	que_thr_t*	thr)
{
	if (rec_get_deleted_flag(clust_rec,
				 dict_table_is_comp(clust_index->table))) {
		/* In delete-marked records, DB_TRX_ID must
		always refer to an existing undo log record. */
		ut_ad(rec_get_trx_id(clust_rec, clust_index));

		/* The clustered index record is delete-marked;
		it is not visible in the read view.  Besides,
		if there are any externally stored columns,
		some of them may have already been purged. */
		return DB_SUCCESS;
	}

	if (dict_index_is_spatial(sec_index)) {
		return row_sel_spatial_sec_rec_is_for_clust_rec(
				sec_rec, sec_index, clust_rec,
				clust_index);
	}

	const byte*	sec_field;
	ulint		sec_len;
	const byte*	clust_field;
	ulint		n;
	ulint		i;
	mem_heap_t*	heap		= mem_heap_create(256);
	rec_offs	clust_offsets_[REC_OFFS_NORMAL_SIZE];
	rec_offs	sec_offsets_[REC_OFFS_SMALL_SIZE];
	rec_offs*	clust_offs	= clust_offsets_;
	rec_offs*	sec_offs	= sec_offsets_;

	rec_offs_init(clust_offsets_);
	rec_offs_init(sec_offsets_);

	ib_vcol_row vc(heap);

	clust_offs = rec_get_offsets(clust_rec, clust_index, clust_offs,
				     clust_index->n_core_fields,
				     ULINT_UNDEFINED, &heap);
	sec_offs = rec_get_offsets(sec_rec, sec_index, sec_offs,
				   sec_index->n_fields,
				   ULINT_UNDEFINED, &heap);

	n = dict_index_get_n_ordering_defined_by_user(sec_index);

	for (i = 0; i < n; i++) {
		const dict_field_t*	ifield;
		const dict_col_t*	col;
		ulint			clust_pos = 0;
		ulint			clust_len = 0;
		ulint			len;

		ifield = dict_index_get_nth_field(sec_index, i);
		col = dict_field_get_col(ifield);

		sec_field = rec_get_nth_field(sec_rec, sec_offs, i, &sec_len);

		const bool is_virtual = col->is_virtual();

		/* For virtual column, its value will need to be
		reconstructed from base column in cluster index */
		if (is_virtual) {
			const dict_v_col_t*	v_col;
			dfield_t*		vfield;
			row_ext_t*		ext;

			byte *record = vc.record(thr_get_trx(thr)->mysql_thd,
						 clust_index,
						 &thr->prebuilt->m_mysql_table);

			v_col = reinterpret_cast<const dict_v_col_t*>(col);

			dtuple_t* row = row_build(
				ROW_COPY_POINTERS,
				clust_index, clust_rec,
				clust_offs,
				NULL, NULL, NULL, &ext, heap);

			vfield = innobase_get_computed_value(
					row, v_col, clust_index,
					&heap, NULL, NULL,
					thr_get_trx(thr)->mysql_thd,
					thr->prebuilt->m_mysql_table,
					record, NULL, NULL,
					true);

			if (vfield == NULL) {
				innobase_report_computed_value_failed(row);
				return DB_COMPUTE_VALUE_FAILED;
			}
			len = clust_len = vfield->len;
			clust_field = static_cast<byte*>(vfield->data);
		} else {
			clust_pos = dict_col_get_clust_pos(col, clust_index);

			clust_field = rec_get_nth_cfield(
				clust_rec, clust_index, clust_offs,
				clust_pos, &clust_len);
			if (clust_len == UNIV_SQL_NULL) {
				if (sec_len == UNIV_SQL_NULL) {
					continue;
				}
				return DB_SUCCESS;
			}
			if (sec_len == UNIV_SQL_NULL) {
				return DB_SUCCESS;
			}

			len = clust_len;
			ulint prefix_len = ifield->prefix_len;
			if (rec_offs_nth_extern(clust_offs, clust_pos)) {
				/* BLOB can contain prefix. */
				len -= BTR_EXTERN_FIELD_REF_SIZE;
				if (!len) {
					goto compare_blobs;
				}
			}

			if (prefix_len) {
				len = dtype_get_at_most_n_mbchars(
					col->prtype, col->mbminlen,
					col->mbmaxlen, prefix_len, len,
					reinterpret_cast<const char*>(
						clust_field));
				if (len < sec_len) {
					goto check_for_blob;
				}
			} else {
check_for_blob:
				if (rec_offs_nth_extern(clust_offs,
							clust_pos)) {
compare_blobs:
					if (!row_sel_sec_rec_is_for_blob(
						    col->mtype, col->prtype,
						    col->mbminlen,
						    col->mbmaxlen,
						    clust_field, clust_len,
						    sec_field, sec_len,
						    prefix_len,
						    clust_index->table)) {
						return DB_SUCCESS;
					}

					continue;
				}
			}
		}

		if (cmp_data(col->mtype, col->prtype, false,
			     clust_field, len, sec_field, sec_len)) {
			return DB_SUCCESS;
		}
	}

	return DB_SUCCESS_LOCKED_REC;
}

/*********************************************************************//**
Creates a select node struct.
@return own: select node struct */
sel_node_t*
sel_node_create(
/*============*/
	mem_heap_t*	heap)	/*!< in: memory heap where created */
{
	sel_node_t*	node;

	node = static_cast<sel_node_t*>(
		mem_heap_alloc(heap, sizeof(sel_node_t)));

	node->common.type = QUE_NODE_SELECT;
	node->state = SEL_NODE_OPEN;

	node->plans = NULL;

	return(node);
}

/*********************************************************************//**
Frees the memory private to a select node when a query graph is freed,
does not free the heap where the node was originally created. */
void
sel_node_free_private(
/*==================*/
	sel_node_t*	node)	/*!< in: select node struct */
{
	ulint	i;
	plan_t*	plan;

	if (node->plans != NULL) {
		for (i = 0; i < node->n_tables; i++) {
			plan = sel_node_get_nth_plan(node, i);

			btr_pcur_close(&(plan->pcur));
			btr_pcur_close(&(plan->clust_pcur));

			if (plan->old_vers_heap) {
				mem_heap_free(plan->old_vers_heap);
			}
		}
	}
}

/*********************************************************************//**
Evaluates the values in a select list. If there are aggregate functions,
their argument value is added to the aggregate total. */
UNIV_INLINE
void
sel_eval_select_list(
/*=================*/
	sel_node_t*	node)	/*!< in: select node */
{
	que_node_t*	exp;

	exp = node->select_list;

	while (exp) {
		eval_exp(exp);

		exp = que_node_get_next(exp);
	}
}

/*********************************************************************//**
Assigns the values in the select list to the possible into-variables in
SELECT ... INTO ... */
UNIV_INLINE
void
sel_assign_into_var_values(
/*=======================*/
	sym_node_t*	var,	/*!< in: first variable in a list of
				variables */
	sel_node_t*	node)	/*!< in: select node */
{
	que_node_t*	exp;

	if (var == NULL) {

		return;
	}

	for (exp = node->select_list;
	     var != 0;
	     var = static_cast<sym_node_t*>(que_node_get_next(var))) {

		ut_ad(exp);

		eval_node_copy_val(var->alias, exp);

		exp = que_node_get_next(exp);
	}
}

/*********************************************************************//**
Resets the aggregate value totals in the select list of an aggregate type
query. */
UNIV_INLINE
void
sel_reset_aggregate_vals(
/*=====================*/
	sel_node_t*	node)	/*!< in: select node */
{
	func_node_t*	func_node;

	ut_ad(node->is_aggregate);

	for (func_node = static_cast<func_node_t*>(node->select_list);
	     func_node != 0;
	     func_node = static_cast<func_node_t*>(
		     	que_node_get_next(func_node))) {

		eval_node_set_int_val(func_node, 0);
	}

	node->aggregate_already_fetched = FALSE;
}

/*********************************************************************//**
Copies the input variable values when an explicit cursor is opened. */
UNIV_INLINE
void
row_sel_copy_input_variable_vals(
/*=============================*/
	sel_node_t*	node)	/*!< in: select node */
{
	sym_node_t*	var;

	var = UT_LIST_GET_FIRST(node->copy_variables);

	while (var) {
		eval_node_copy_val(var, var->alias);

		var->indirection = NULL;

		var = UT_LIST_GET_NEXT(col_var_list, var);
	}
}

/*********************************************************************//**
Fetches the column values from a record. */
static
void
row_sel_fetch_columns(
/*==================*/
	dict_index_t*	index,	/*!< in: record index */
	const rec_t*	rec,	/*!< in: record in a clustered or non-clustered
				index; must be protected by a page latch */
	const rec_offs*	offsets,/*!< in: rec_get_offsets(rec, index) */
	sym_node_t*	column)	/*!< in: first column in a column list, or
				NULL */
{
	dfield_t*	val;
	ulint		index_type;
	ulint		field_no;
	const byte*	data;
	ulint		len;

	ut_ad(rec_offs_validate(rec, index, offsets));

	if (dict_index_is_clust(index)) {
		index_type = SYM_CLUST_FIELD_NO;
	} else {
		index_type = SYM_SEC_FIELD_NO;
	}

	while (column) {
		mem_heap_t*	heap = NULL;
		ibool		needs_copy;

		field_no = column->field_nos[index_type];

		if (field_no != ULINT_UNDEFINED) {

			if (UNIV_UNLIKELY(rec_offs_nth_extern(
						  offsets, field_no) != 0)) {

				/* Copy an externally stored field to the
				temporary heap, if possible. */

				heap = mem_heap_create(1);

				data = btr_rec_copy_externally_stored_field(
					rec, offsets,
					index->table->space->zip_size(),
					field_no, &len, heap);

				/* data == NULL means that the
				externally stored field was not
				written yet. This record
				should only be seen by
				trx_rollback_recovered() or any
				TRX_ISO_READ_UNCOMMITTED
				transactions. The InnoDB SQL parser
				(the sole caller of this function)
				does not implement READ UNCOMMITTED,
				and it is not involved during rollback. */
				ut_a(data);
				ut_a(len != UNIV_SQL_NULL);

				needs_copy = TRUE;
			} else {
				data = rec_get_nth_cfield(rec, index, offsets,
							  field_no, &len);
				needs_copy = column->copy_val;
			}

			if (needs_copy) {
				eval_node_copy_and_alloc_val(column, data,
							     len);
			} else {
				val = que_node_get_val(column);
				dfield_set_data(val, data, len);
			}

			if (UNIV_LIKELY_NULL(heap)) {
				mem_heap_free(heap);
			}
		}

		column = UT_LIST_GET_NEXT(col_var_list, column);
	}
}

/*********************************************************************//**
Allocates a prefetch buffer for a column when prefetch is first time done. */
static
void
sel_col_prefetch_buf_alloc(
/*=======================*/
	sym_node_t*	column)	/*!< in: symbol table node for a column */
{
	sel_buf_t*	sel_buf;
	ulint		i;

	ut_ad(que_node_get_type(column) == QUE_NODE_SYMBOL);

	column->prefetch_buf = static_cast<sel_buf_t*>(
		ut_malloc_nokey(SEL_MAX_N_PREFETCH * sizeof(sel_buf_t)));

	for (i = 0; i < SEL_MAX_N_PREFETCH; i++) {
		sel_buf = column->prefetch_buf + i;

		sel_buf->data = NULL;
		sel_buf->len = 0;
		sel_buf->val_buf_size = 0;
	}
}

/*********************************************************************//**
Frees a prefetch buffer for a column, including the dynamically allocated
memory for data stored there. */
void
sel_col_prefetch_buf_free(
/*======================*/
	sel_buf_t*	prefetch_buf)	/*!< in, own: prefetch buffer */
{
	sel_buf_t*	sel_buf;
	ulint		i;

	for (i = 0; i < SEL_MAX_N_PREFETCH; i++) {
		sel_buf = prefetch_buf + i;

		if (sel_buf->val_buf_size > 0) {

			ut_free(sel_buf->data);
		}
	}

	ut_free(prefetch_buf);
}

/*********************************************************************//**
Pops the column values for a prefetched, cached row from the column prefetch
buffers and places them to the val fields in the column nodes. */
static
void
sel_dequeue_prefetched_row(
/*=======================*/
	plan_t*	plan)	/*!< in: plan node for a table */
{
	sym_node_t*	column;
	sel_buf_t*	sel_buf;
	dfield_t*	val;
	byte*		data;
	ulint		len;
	ulint		val_buf_size;

	ut_ad(plan->n_rows_prefetched > 0);

	column = UT_LIST_GET_FIRST(plan->columns);

	while (column) {
		val = que_node_get_val(column);

		if (!column->copy_val) {
			/* We did not really push any value for the
			column */

			ut_ad(!column->prefetch_buf);
			ut_ad(que_node_get_val_buf_size(column) == 0);
			ut_d(dfield_set_null(val));

			goto next_col;
		}

		ut_ad(column->prefetch_buf);
		ut_ad(!dfield_is_ext(val));

		sel_buf = column->prefetch_buf + plan->first_prefetched;

		data = sel_buf->data;
		len = sel_buf->len;
		val_buf_size = sel_buf->val_buf_size;

		/* We must keep track of the allocated memory for
		column values to be able to free it later: therefore
		we swap the values for sel_buf and val */

		sel_buf->data = static_cast<byte*>(dfield_get_data(val));
		sel_buf->len = dfield_get_len(val);
		sel_buf->val_buf_size = que_node_get_val_buf_size(column);

		dfield_set_data(val, data, len);
		que_node_set_val_buf_size(column, val_buf_size);
next_col:
		column = UT_LIST_GET_NEXT(col_var_list, column);
	}

	plan->n_rows_prefetched--;

	plan->first_prefetched++;
}

/*********************************************************************//**
Pushes the column values for a prefetched, cached row to the column prefetch
buffers from the val fields in the column nodes. */
UNIV_INLINE
void
sel_enqueue_prefetched_row(
/*=======================*/
	plan_t*	plan)	/*!< in: plan node for a table */
{
	sym_node_t*	column;
	sel_buf_t*	sel_buf;
	dfield_t*	val;
	byte*		data;
	ulint		len;
	ulint		pos;
	ulint		val_buf_size;

	if (plan->n_rows_prefetched == 0) {
		pos = 0;
		plan->first_prefetched = 0;
	} else {
		pos = plan->n_rows_prefetched;

		/* We have the convention that pushing new rows starts only
		after the prefetch stack has been emptied: */

		ut_ad(plan->first_prefetched == 0);
	}

	plan->n_rows_prefetched++;

	ut_ad(pos < SEL_MAX_N_PREFETCH);

	for (column = UT_LIST_GET_FIRST(plan->columns);
	     column != 0;
	     column = UT_LIST_GET_NEXT(col_var_list, column)) {

		if (!column->copy_val) {
			/* There is no sense to push pointers to database
			page fields when we do not keep latch on the page! */
			continue;
		}

		if (!column->prefetch_buf) {
			/* Allocate a new prefetch buffer */

			sel_col_prefetch_buf_alloc(column);
		}

		sel_buf = column->prefetch_buf + pos;

		val = que_node_get_val(column);

		data = static_cast<byte*>(dfield_get_data(val));
		len = dfield_get_len(val);
		val_buf_size = que_node_get_val_buf_size(column);

		/* We must keep track of the allocated memory for
		column values to be able to free it later: therefore
		we swap the values for sel_buf and val */

		dfield_set_data(val, sel_buf->data, sel_buf->len);
		que_node_set_val_buf_size(column, sel_buf->val_buf_size);

		sel_buf->data = data;
		sel_buf->len = len;
		sel_buf->val_buf_size = val_buf_size;
	}
}

/*********************************************************************//**
Builds a previous version of a clustered index record for a consistent read
@return DB_SUCCESS or error code */
static MY_ATTRIBUTE((nonnull, warn_unused_result))
dberr_t
row_sel_build_prev_vers(
/*====================*/
	ReadView*	read_view,	/*!< in: read view */
	dict_index_t*	index,		/*!< in: plan node for table */
	rec_t*		rec,		/*!< in: record in a clustered index */
	rec_offs**	offsets,	/*!< in/out: offsets returned by
					rec_get_offsets(rec, plan->index) */
	mem_heap_t**	offset_heap,	/*!< in/out: memory heap from which
					the offsets are allocated */
	mem_heap_t**    old_vers_heap,  /*!< out: old version heap to use */
	rec_t**		old_vers,	/*!< out: old version, or NULL if the
					record does not exist in the view:
					i.e., it was freshly inserted
					afterwards */
	mtr_t*		mtr)		/*!< in: mtr */
{
	dberr_t	err;

	if (*old_vers_heap) {
		mem_heap_empty(*old_vers_heap);
	} else {
		*old_vers_heap = mem_heap_create(512);
	}

	err = row_vers_build_for_consistent_read(
		rec, mtr, index, offsets, read_view, offset_heap,
		*old_vers_heap, old_vers, NULL);
	return(err);
}

/*********************************************************************//**
Builds the last committed version of a clustered index record for a
semi-consistent read. */
static
void
row_sel_build_committed_vers_for_mysql(
/*===================================*/
	dict_index_t*	clust_index,	/*!< in: clustered index */
	row_prebuilt_t*	prebuilt,	/*!< in: prebuilt struct */
	const rec_t*	rec,		/*!< in: record in a clustered index */
	rec_offs**	offsets,	/*!< in/out: offsets returned by
					rec_get_offsets(rec, clust_index) */
	mem_heap_t**	offset_heap,	/*!< in/out: memory heap from which
					the offsets are allocated */
	const rec_t**	old_vers,	/*!< out: old version, or NULL if the
					record does not exist in the view:
					i.e., it was freshly inserted
					afterwards */
	dtuple_t**	vrow,		/*!< out: to be filled with old virtual
					column version if any */
	mtr_t*		mtr)		/*!< in: mtr */
{
	if (prebuilt->trx->snapshot_isolation) {
		ut_ad(prebuilt->trx->isolation_level
		    == TRX_ISO_READ_UNCOMMITTED);
		*old_vers = rec;
		return;
	}

	if (prebuilt->old_vers_heap) {
		mem_heap_empty(prebuilt->old_vers_heap);
	} else {
		prebuilt->old_vers_heap = mem_heap_create(
			rec_offs_size(*offsets));
	}

	row_vers_build_for_semi_consistent_read(
		rec, mtr, clust_index, offsets, offset_heap,
		prebuilt->old_vers_heap, old_vers, vrow);
}

/*********************************************************************//**
Tests the conditions which determine when the index segment we are searching
through has been exhausted.
@return TRUE if row passed the tests */
UNIV_INLINE
ibool
row_sel_test_end_conds(
/*===================*/
	plan_t*	plan)	/*!< in: plan for the table; the column values must
			already have been retrieved and the right sides of
			comparisons evaluated */
{
	func_node_t*	cond;

	/* All conditions in end_conds are comparisons of a column to an
	expression */

	for (cond = UT_LIST_GET_FIRST(plan->end_conds);
	     cond != 0;
	     cond = UT_LIST_GET_NEXT(cond_list, cond)) {

		/* Evaluate the left side of the comparison, i.e., get the
		column value if there is an indirection */

		eval_sym(static_cast<sym_node_t*>(cond->args));

		/* Do the comparison */

		if (!eval_cmp(cond)) {

			return(FALSE);
		}
	}

	return(TRUE);
}

/*********************************************************************//**
Tests the other conditions.
@return TRUE if row passed the tests */
UNIV_INLINE
ibool
row_sel_test_other_conds(
/*=====================*/
	plan_t*	plan)	/*!< in: plan for the table; the column values must
			already have been retrieved */
{
	func_node_t*	cond;

	cond = UT_LIST_GET_FIRST(plan->other_conds);

	while (cond) {
		eval_exp(cond);

		if (!eval_node_get_ibool_val(cond)) {

			return(FALSE);
		}

		cond = UT_LIST_GET_NEXT(cond_list, cond);
	}

	return(TRUE);
}

/** Check that a clustered index record is visible in a consistent read view.
@param rec      clustered index record (in leaf page, or in memory)
@param index    clustered index
@param offsets  rec_get_offsets(rec, index)
@param view     consistent read view
@retval DB_SUCCESS             if rec is visible in view
@retval DB_SUCCESS_LOCKED_REC  if rec is not visible in view
@retval DB_CORRUPTION          if the DB_TRX_ID is corrupted */
static dberr_t row_sel_clust_sees(const rec_t *rec, const dict_index_t &index,
                                  const rec_offs *offsets,
                                  const ReadView &view)
{
  ut_ad(index.is_primary());
  ut_ad(page_rec_is_user_rec(rec));
  ut_ad(rec_offs_validate(rec, &index, offsets));
  ut_ad(!rec_is_metadata(rec, index));
  ut_ad(!index.table->is_temporary());

  const trx_id_t id= row_get_rec_trx_id(rec, &index, offsets);

  if (view.changes_visible(id))
    return DB_SUCCESS;
  if (UNIV_LIKELY(id < view.low_limit_id() || id < trx_sys.get_max_trx_id()))
    return DB_SUCCESS_LOCKED_REC;

  ib::warn() << "A transaction id in a record of table " << index.table->name
             << " is newer than the system-wide maximum.";
  return DB_CORRUPTION;
}

/*********************************************************************//**
Retrieves the clustered index record corresponding to a record in a
non-clustered index. Does the necessary locking.
@return DB_SUCCESS or error code */
static MY_ATTRIBUTE((nonnull, warn_unused_result))
dberr_t
row_sel_get_clust_rec(
/*==================*/
	sel_node_t*	node,	/*!< in: select_node */
	plan_t*		plan,	/*!< in: plan node for table */
	rec_t*		rec,	/*!< in: record in a non-clustered index */
	que_thr_t*	thr,	/*!< in: query thread */
	rec_t**		out_rec,/*!< out: clustered record or an old version of
				it, NULL if the old version did not exist
				in the read view, i.e., it was a fresh
				inserted version */
	mtr_t*		mtr)	/*!< in: mtr used to get access to the
				non-clustered record; the same mtr is used to
				access the clustered index */
{
	dict_index_t*	index;
	rec_t*		clust_rec;
	rec_t*		old_vers;
	mem_heap_t*	heap		= NULL;
	rec_offs	offsets_[REC_OFFS_NORMAL_SIZE];
	rec_offs*	offsets		= offsets_;
	rec_offs_init(offsets_);

	*out_rec = NULL;

	offsets = rec_get_offsets(rec, plan->pcur.index(), offsets,
				  plan->pcur.index()->n_core_fields,
				  ULINT_UNDEFINED, &heap);

	row_build_row_ref_fast(plan->clust_ref, plan->clust_map, rec, offsets);

	index = dict_table_get_first_index(plan->table);
	plan->clust_pcur.old_rec = nullptr;
	plan->clust_pcur.btr_cur.page_cur.index = index;
	dberr_t err = btr_pcur_open_with_no_init(plan->clust_ref,
						 PAGE_CUR_LE, BTR_SEARCH_LEAF,
						 &plan->clust_pcur, mtr);
	if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
		goto err_exit;
	}

	clust_rec = btr_pcur_get_rec(&(plan->clust_pcur));

	/* Note: only if the search ends up on a non-infimum record is the
	low_match value the real match to the search tuple */

	if (!page_rec_is_user_rec(clust_rec)
	    || btr_pcur_get_low_match(&(plan->clust_pcur))
	    < dict_index_get_n_unique(index)) {

		if (!node->read_view ||
		    !rec_get_deleted_flag(rec, plan->table->not_redundant())) {
			err = DB_CORRUPTION;
		}

		/* In a rare case it is possible that no clust rec is found
		for a delete-marked secondary index record: if in row0umod.cc
		in row_undo_mod_remove_clust_low() we have already removed
		the clust rec, while purge is still cleaning and removing
		secondary index records associated with earlier versions of
		the clustered index record. In that case we know that the
		clustered index record did not exist in the read view of
		trx. */

		goto err_exit;
	}

	offsets = rec_get_offsets(clust_rec, index, offsets,
				  index->n_core_fields,
				  ULINT_UNDEFINED, &heap);

	if (!node->read_view) {
		/* Try to place a lock on the index record */
		trx_t* trx = thr_get_trx(thr);

		/* At READ UNCOMMITTED or READ COMMITTED isolation level
		we lock only the record, i.e., next-key locking is
		not used. */
		err = lock_clust_rec_read_check_and_lock(
			0, btr_pcur_get_block(&plan->clust_pcur),
			clust_rec, index, offsets,
			node->row_lock_mode,
			trx->isolation_level <= TRX_ISO_READ_COMMITTED
			? LOCK_REC_NOT_GAP : LOCK_ORDINARY,
			thr);

		switch (err) {
		case DB_SUCCESS:
		case DB_SUCCESS_LOCKED_REC:
			/* Declare the variable uninitialized.
			It should be set to DB_SUCCESS at func_exit. */
			MEM_UNDEFINED(&err, sizeof err);
			break;
		default:
			goto err_exit;
		}
	} else {
		/* This is a non-locking consistent read: if necessary, fetch
		a previous version of the record */

		old_vers = NULL;

		err = row_sel_clust_sees(clust_rec, *index, offsets,
                                         *node->read_view);

		switch (err) {
		default:
			goto err_exit;
		case DB_SUCCESS:
			break;
		case DB_SUCCESS_LOCKED_REC:
			err = row_sel_build_prev_vers(
				node->read_view, index, clust_rec,
				&offsets, &heap, &plan->old_vers_heap,
				&old_vers, mtr);

			if (err != DB_SUCCESS) {

				goto err_exit;
			}

			clust_rec = old_vers;

			if (clust_rec == NULL) {
				goto err_exit;
			}
		}

		/* If we had to go to an earlier version of row or the
		secondary index record is delete marked, then it may be that
		the secondary index record corresponding to clust_rec
		(or old_vers) is not rec; in that case we must ignore
		such row because in our snapshot rec would not have existed.
		Remember that from rec we cannot see directly which transaction
		id corresponds to it: we have to go to the clustered index
		record. A query where we want to fetch all rows where
		the secondary index value is in some interval would return
		a wrong result if we would not drop rows which we come to
		visit through secondary index records that would not really
		exist in our snapshot. */

		if (old_vers || rec_get_deleted_flag(rec, dict_table_is_comp(
							       plan->table))) {
			err = row_sel_sec_rec_is_for_clust_rec(rec,
							plan->index, clust_rec,
							index, thr);
			if (err != DB_SUCCESS_LOCKED_REC) {
				goto err_exit;
			}
		}
	}

	/* Fetch the columns needed in test conditions.  The clustered
	index record is protected by a page latch that was acquired
	when plan->clust_pcur was positioned.  The latch will not be
	released until mtr->commit(). */

	ut_ad(!rec_get_deleted_flag(clust_rec, rec_offs_comp(offsets)));
	row_sel_fetch_columns(index, clust_rec, offsets,
			      UT_LIST_GET_FIRST(plan->columns));
	*out_rec = clust_rec;
	err = DB_SUCCESS;
err_exit:
	if (UNIV_LIKELY_NULL(heap)) {
		mem_heap_free(heap);
	}
	return(err);
}

/*********************************************************************//**
Sets a lock on a page of R-Tree record. This is all or none action,
mostly due to we cannot reposition a record in R-Tree (with the
nature of splitting)
@return DB_SUCCESS, DB_SUCCESS_LOCKED_REC, or error code */
UNIV_INLINE
dberr_t
sel_set_rtr_rec_lock(
/*=================*/
	btr_pcur_t*		pcur,	/*!< in: cursor */
	const rec_t*		first_rec,/*!< in: record */
	dict_index_t*		index,	/*!< in: index */
	const rec_offs*		offsets,/*!< in: rec_get_offsets(rec, index) */
	unsigned		mode,	/*!< in: lock mode */
	unsigned		type,	/*!< in: LOCK_ORDINARY, LOCK_GAP, or
					LOC_REC_NOT_GAP */
	que_thr_t*		thr,	/*!< in: query thread */
	mtr_t*			mtr)	/*!< in: mtr */
{
	matched_rec_t*  match = pcur->btr_cur.rtr_info->matches;
	mem_heap_t*     heap = NULL;
	dberr_t		err = DB_SUCCESS;
	trx_t*		trx = thr_get_trx(thr);
	buf_block_t*	cur_block = btr_pcur_get_block(pcur);
	rec_offs	offsets_[REC_OFFS_NORMAL_SIZE];
	rec_offs*	my_offsets = const_cast<rec_offs*>(offsets);
	rec_t*		rec = const_cast<rec_t*>(first_rec);
	rtr_rec_vector*	match_rec;
	rtr_rec_vector::iterator end;

	rec_offs_init(offsets_);

	if (match->locked || page_rec_is_supremum(first_rec)) {
		return(DB_SUCCESS_LOCKED_REC);
	}

	ut_ad(page_align(first_rec) == cur_block->page.frame);
	ut_ad(match->valid);

	match->block->page.lock.x_lock();
retry:
	cur_block = btr_pcur_get_block(pcur);
	ut_ad(match->block->page.lock.have_x()
	      || match->block->page.lock.have_s());
	ut_ad(page_is_leaf(cur_block->page.frame));

	err = lock_sec_rec_read_check_and_lock(
		0, cur_block, rec, index, my_offsets,
		static_cast<lock_mode>(mode), type, thr);

	if (err == DB_LOCK_WAIT) {
re_scan:
		mtr->commit();
		trx->error_state = err;
		thr->lock_state = QUE_THR_LOCK_ROW;
		if (row_mysql_handle_errors(&err, trx, thr, 0)) {
			thr->lock_state = QUE_THR_LOCK_NOLOCK;
			mtr->start();

			mysql_mutex_lock(&match->rtr_match_mutex);
			if (!match->valid && match->matched_recs->empty()) {
				mysql_mutex_unlock(&match->rtr_match_mutex);
				err = DB_RECORD_NOT_FOUND;
				goto func_end;
			}
			mysql_mutex_unlock(&match->rtr_match_mutex);

			/* MDEV-14059 FIXME: why re-latch the block?
			pcur is already positioned on it! */
			cur_block = buf_page_get_gen(
				btr_pcur_get_block(pcur)->page.id(),
				btr_pcur_get_block(pcur)->zip_size(),
				RW_X_LATCH, NULL, BUF_GET, mtr, &err);
			if (!cur_block) {
				goto func_end;
			}
			buf_page_make_young_if_needed(&cur_block->page);
		} else {
			mtr->start();
			goto func_end;
		}

		DEBUG_SYNC_C("rtr_set_lock_wait");

		if (!match->valid) {
			/* Page got deleted */
			mtr->commit();
			mtr->start();
			err = DB_RECORD_NOT_FOUND;
			goto func_end;
		}

		match->matched_recs->clear();
		// FIXME: check for !cur_block

		rtr_cur_search_with_match(
			cur_block, index,
			pcur->btr_cur.rtr_info->search_tuple,
			pcur->btr_cur.rtr_info->search_mode,
			&pcur->btr_cur.page_cur,
			pcur->btr_cur.rtr_info);

		if (!page_is_leaf(buf_block_get_frame(cur_block))) {
			/* Page got splitted and promoted (only for
			root page it is possible).  Release the
			page and ask for a re-search */
			mtr->commit();
			mtr->start();
			err = DB_RECORD_NOT_FOUND;
			goto func_end;
		}

		rec = btr_pcur_get_rec(pcur);
		my_offsets = offsets_;
		my_offsets = rec_get_offsets(rec, index, my_offsets,
					     index->n_fields,
					     ULINT_UNDEFINED, &heap);

		/* No match record */
		if (page_rec_is_supremum(rec) || !match->valid) {
			mtr->commit();
			mtr->start();
			err = DB_RECORD_NOT_FOUND;
			goto func_end;
		}

		goto retry;
	}

	my_offsets = offsets_;
	match_rec = match->matched_recs;
	end = match_rec->end();

	for (rtr_rec_vector::iterator it = match_rec->begin();
	     it != end; ++it) {
		rtr_rec_t*	rtr_rec = &(*it);

		my_offsets = rec_get_offsets(
			rtr_rec->r_rec, index, my_offsets, index->n_fields,
			ULINT_UNDEFINED, &heap);

		err = lock_sec_rec_read_check_and_lock(
			0, match->block, rtr_rec->r_rec, index,
			my_offsets, static_cast<lock_mode>(mode),
			type, thr);

		if (err == DB_SUCCESS || err == DB_SUCCESS_LOCKED_REC) {
			rtr_rec->locked = true;
		} else if (err == DB_LOCK_WAIT) {
			goto re_scan;
		} else {
			goto func_end;
		}
	}

	match->locked = true;

func_end:
	match->block->page.lock.x_unlock();
	if (heap != NULL) {
		mem_heap_free(heap);
	}

	ut_ad(err != DB_LOCK_WAIT);

	return(err);
}

/*********************************************************************//**
Sets a lock on a record.
@return DB_SUCCESS, DB_SUCCESS_LOCKED_REC, or error code */
UNIV_INLINE
dberr_t
sel_set_rec_lock(
/*=============*/
	btr_pcur_t*		pcur,	/*!< in: cursor */
	const rec_t*		rec,	/*!< in: record */
	dict_index_t*		index,	/*!< in: index */
	const rec_offs*		offsets,/*!< in: rec_get_offsets(rec, index) */
	unsigned		mode,	/*!< in: lock mode */
	unsigned		type,	/*!< in: LOCK_ORDINARY, LOCK_GAP, or
					LOC_REC_NOT_GAP */
	que_thr_t*		thr,	/*!< in: query thread */
	mtr_t*			mtr)	/*!< in: mtr */
{
	trx_t*			trx;
	dberr_t			err = DB_SUCCESS;
	const buf_block_t*	block;

	block = btr_pcur_get_block(pcur);

	trx = thr_get_trx(thr);

	if (UT_LIST_GET_LEN(trx->lock.trx_locks) > 10000
	    && buf_pool.running_out()) {
		return DB_LOCK_TABLE_FULL;
	}

	if (dict_index_is_clust(index)) {
		err = lock_clust_rec_read_check_and_lock(
			0, block, rec, index, offsets,
			static_cast<lock_mode>(mode), type, thr);
	} else {

		if (dict_index_is_spatial(index)) {
			if (type == LOCK_GAP || type == LOCK_ORDINARY) {
				ut_ad(0);
				ib::error() << "Incorrectly request GAP lock "
					"on RTree";
				return(DB_SUCCESS);
			}
			err = sel_set_rtr_rec_lock(pcur, rec, index, offsets,
						   mode, type, thr, mtr);
		} else {
			err = lock_sec_rec_read_check_and_lock(
				0, block, rec, index, offsets,
				static_cast<lock_mode>(mode), type, thr);
		}
	}

	return(err);
}

/*********************************************************************//**
Opens a pcur to a table index. */
MY_ATTRIBUTE((warn_unused_result, nonnull))
static
dberr_t
row_sel_open_pcur(
/*==============*/
	plan_t*		plan,	/*!< in: table plan */
	mtr_t*		mtr)	/*!< in/out: mini-transaction */
{
	dict_index_t*	index;
	func_node_t*	cond;
	que_node_t*	exp;
	ulint		n_fields;
	ulint		i;

	ut_ad(!plan->n_rows_prefetched);
	ut_ad(!plan->n_rows_fetched);
	ut_ad(!plan->cursor_at_end);

	index = plan->index;

	/* Calculate the value of the search tuple: the exact match columns
	get their expressions evaluated when we evaluate the right sides of
	end_conds */

	cond = UT_LIST_GET_FIRST(plan->end_conds);

	while (cond) {
		eval_exp(que_node_get_next(cond->args));

		cond = UT_LIST_GET_NEXT(cond_list, cond);
	}

	plan->pcur.old_rec = nullptr;
	plan->pcur.btr_cur.page_cur.index = index;

	dberr_t err;

	if (plan->tuple) {
		n_fields = dtuple_get_n_fields(plan->tuple);

		if (plan->n_exact_match < n_fields) {
			/* There is a non-exact match field which must be
			evaluated separately */

			eval_exp(plan->tuple_exps[n_fields - 1]);
		}

		for (i = 0; i < n_fields; i++) {
			exp = plan->tuple_exps[i];

			dfield_copy_data(dtuple_get_nth_field(plan->tuple, i),
					 que_node_get_val(exp));
		}

		err = btr_pcur_open_with_no_init(plan->tuple,
						 plan->mode, BTR_SEARCH_LEAF,
						 &plan->pcur, mtr);
	} else {
		err = plan->pcur.open_leaf(plan->asc, index, BTR_SEARCH_LEAF,
					   mtr);
	}

	plan->pcur_is_open = err == DB_SUCCESS;
	return err;
}

/*********************************************************************//**
Restores a stored pcur position to a table index.
@return TRUE if the cursor should be moved to the next record after we
return from this function (moved to the previous, in the case of a
descending cursor) without processing again the current cursor
record */
static
ibool
row_sel_restore_pcur_pos(
/*=====================*/
	plan_t*		plan,	/*!< in: table plan */
	mtr_t*		mtr)	/*!< in: mtr */
{
	ibool	equal_position;
	ulint	relative_position;

	ut_ad(!plan->cursor_at_end);

	relative_position = btr_pcur_get_rel_pos(&(plan->pcur));

	equal_position =
	  plan->pcur.restore_position(BTR_SEARCH_LEAF, mtr) ==
	  btr_pcur_t::SAME_ALL;

	/* If the cursor is traveling upwards, and relative_position is

	(1) BTR_PCUR_BEFORE: this is not allowed, as we did not have a lock
	yet on the successor of the page infimum;
	(2) BTR_PCUR_AFTER: btr_pcur_restore_position placed the cursor on the
	first record GREATER than the predecessor of a page supremum; we have
	not yet processed the cursor record: no need to move the cursor to the
	next record;
	(3) BTR_PCUR_ON: btr_pcur_restore_position placed the cursor on the
	last record LESS or EQUAL to the old stored user record; (a) if
	equal_position is FALSE, this means that the cursor is now on a record
	less than the old user record, and we must move to the next record;
	(b) if equal_position is TRUE, then if
	plan->stored_cursor_rec_processed is TRUE, we must move to the next
	record, else there is no need to move the cursor. */

	if (plan->asc) {
		if (relative_position == BTR_PCUR_ON) {

			if (equal_position) {

				return(plan->stored_cursor_rec_processed);
			}

			return(TRUE);
		}

		ut_ad(relative_position == BTR_PCUR_AFTER
		      || relative_position == BTR_PCUR_AFTER_LAST_IN_TREE);

		return(FALSE);
	}

	/* If the cursor is traveling downwards, and relative_position is

	(1) BTR_PCUR_BEFORE: btr_pcur_restore_position placed the cursor on
	the last record LESS than the successor of a page infimum; we have not
	processed the cursor record: no need to move the cursor;
	(2) BTR_PCUR_AFTER: btr_pcur_restore_position placed the cursor on the
	first record GREATER than the predecessor of a page supremum; we have
	processed the cursor record: we should move the cursor to the previous
	record;
	(3) BTR_PCUR_ON: btr_pcur_restore_position placed the cursor on the
	last record LESS or EQUAL to the old stored user record; (a) if
	equal_position is FALSE, this means that the cursor is now on a record
	less than the old user record, and we need not move to the previous
	record; (b) if equal_position is TRUE, then if
	plan->stored_cursor_rec_processed is TRUE, we must move to the previous
	record, else there is no need to move the cursor. */

	if (relative_position == BTR_PCUR_BEFORE
	    || relative_position == BTR_PCUR_BEFORE_FIRST_IN_TREE) {

		return(FALSE);
	}

	if (relative_position == BTR_PCUR_ON) {

		if (equal_position) {

			return(plan->stored_cursor_rec_processed);
		}

		return(FALSE);
	}

	ut_ad(relative_position == BTR_PCUR_AFTER
	      || relative_position == BTR_PCUR_AFTER_LAST_IN_TREE);

	return(TRUE);
}

/*********************************************************************//**
Resets a plan cursor to a closed state. */
UNIV_INLINE
void
plan_reset_cursor(
/*==============*/
	plan_t*	plan)	/*!< in: plan */
{
	plan->pcur_is_open = FALSE;
	plan->cursor_at_end = FALSE;
	plan->n_rows_fetched = 0;
	plan->n_rows_prefetched = 0;
}

#ifdef BTR_CUR_HASH_ADAPT
/*********************************************************************//**
Tries to do a shortcut to fetch a clustered index record with a unique key,
using the hash index if possible (not always).
@return SEL_FOUND, SEL_EXHAUSTED, SEL_RETRY */
static
ulint
row_sel_try_search_shortcut(
/*========================*/
	sel_node_t*	node,	/*!< in: select node for a consistent read */
	plan_t*		plan,	/*!< in: plan for a unique search in clustered
				index */
	mtr_t*		mtr)	/*!< in: mtr */
{
	dict_index_t*	index = plan->index;

	ut_ad(!index->table->is_temporary());
	ut_ad(node->read_view);
	ut_ad(node->read_view->is_open());
	ut_ad(plan->unique_search);
	ut_ad(!plan->must_get_clust);

	if (row_sel_open_pcur(plan, mtr) != DB_SUCCESS) {
		return SEL_RETRY;
	}

	const rec_t* rec = btr_pcur_get_rec(&(plan->pcur));

	if (!page_rec_is_user_rec(rec) || rec_is_metadata(rec, *index)) {
		return SEL_RETRY;
	}

	ut_ad(plan->mode == PAGE_CUR_GE);

	/* As the cursor is now placed on a user record after a search with
	the mode PAGE_CUR_GE, the up_match field in the cursor tells how many
	fields in the user record matched to the search tuple */

	if (btr_pcur_get_up_match(&(plan->pcur)) < plan->n_exact_match) {
		return SEL_EXHAUSTED;
	}

	if (trx_id_t bulk_trx_id = index->table->bulk_trx_id) {
		/* See row_search_mvcc() for a comment on bulk_trx_id */
		if (!node->read_view->changes_visible(bulk_trx_id)) {
			return SEL_EXHAUSTED;
		}
	}

	/* This is a non-locking consistent read: if necessary, fetch
	a previous version of the record */

	mem_heap_t*	heap		= NULL;
	rec_offs	offsets_[REC_OFFS_NORMAL_SIZE];
	rec_offs*	offsets		= offsets_;
	rec_offs_init(offsets_);
	offsets = rec_get_offsets(rec, index, offsets, index->n_core_fields,
				  ULINT_UNDEFINED, &heap);

	if (dict_index_is_clust(index)) {
		if (row_sel_clust_sees(rec, *index, offsets, *node->read_view)
		    != DB_SUCCESS) {
			return SEL_RETRY;
		}
	} else if (!srv_read_only_mode) {
		trx_id_t trx_id =
			page_get_max_trx_id(btr_pcur_get_page(&plan->pcur));
		ut_ad(trx_id);
		if (!node->read_view->sees(trx_id)) {
			return SEL_RETRY;
		}
	}

	if (rec_get_deleted_flag(rec, dict_table_is_comp(plan->table))) {
		return SEL_EXHAUSTED;
	}

	/* Fetch the columns needed in test conditions.  The index
	record is protected by a page latch that was acquired when
	plan->pcur was positioned.  The latch will not be released
	until mtr->commit(). */

	row_sel_fetch_columns(index, rec, offsets,
			      UT_LIST_GET_FIRST(plan->columns));

	/* Test the rest of search conditions */

	if (!row_sel_test_other_conds(plan)) {
		return SEL_EXHAUSTED;
	}

	ut_ad(plan->pcur.latch_mode == BTR_SEARCH_LEAF);

	plan->n_rows_fetched++;

	if (UNIV_LIKELY_NULL(heap)) {
		mem_heap_free(heap);
	}
	return SEL_FOUND;
}
#endif /* BTR_CUR_HASH_ADAPT */

/*********************************************************************//**
Performs a select step.
@return DB_SUCCESS or error code */
static MY_ATTRIBUTE((warn_unused_result))
dberr_t
row_sel(
/*====*/
	sel_node_t*	node,	/*!< in: select node */
	que_thr_t*	thr)	/*!< in: query thread */
{
	dict_index_t*	index;
	plan_t*		plan;
	mtr_t		mtr{thr_get_trx(thr)};
	ibool		moved;
	rec_t*		rec;
	rec_t*		old_vers;
	rec_t*		clust_rec;

	/* The following flag becomes TRUE when we are doing a
	consistent read from a non-clustered index and we must look
	at the clustered index to find out the previous delete mark
	state of the non-clustered record: */

	ibool		cons_read_requires_clust_rec	= FALSE;
	ulint		cost_counter			= 0;
	ibool		cursor_just_opened;
	ibool		must_go_to_next;
	ibool		mtr_has_extra_clust_latch	= FALSE;
	/* TRUE if the search was made using
	a non-clustered index, and we had to
	access the clustered record: now &mtr
	contains a clustered index latch, and
	&mtr must be committed before we move
	to the next non-clustered record */
	dberr_t		err;
	mem_heap_t*	heap				= NULL;
	rec_offs	offsets_[REC_OFFS_NORMAL_SIZE];
	rec_offs*	offsets				= offsets_;
	rec_offs_init(offsets_);
	const trx_t*	trx = thr_get_trx(thr);

	ut_ad(thr->run_node == node);
	ut_ad(!node->read_view || node->read_view == &trx->read_view);
	ut_ad(!node->read_view || node->read_view->is_open());

table_loop:
	/* TABLE LOOP
	----------
	This is the outer major loop in calculating a join. We come here when
	node->fetch_table changes, and after adding a row to aggregate totals
	and, of course, when this function is called. */

	ut_ad(mtr_has_extra_clust_latch == FALSE);

	plan = sel_node_get_nth_plan(node, node->fetch_table);
	index = plan->index;

	if (plan->n_rows_prefetched > 0) {
		sel_dequeue_prefetched_row(plan);

		goto next_table_no_mtr;
	}

	if (plan->cursor_at_end) {
		/* The cursor has already reached the result set end: no more
		rows to process for this table cursor, as also the prefetch
		stack was empty */

		ut_ad(plan->pcur_is_open);

		goto table_exhausted_no_mtr;
	}

	/* Open a cursor to index, or restore an open cursor position */

	mtr.start();

#ifdef BTR_CUR_HASH_ADAPT
	if (node->read_view && plan->unique_search && !plan->pcur_is_open
	    && !plan->must_get_clust) {
		switch (row_sel_try_search_shortcut(node, plan, &mtr)) {
		case SEL_FOUND:
			goto next_table;
		case SEL_EXHAUSTED:
			goto table_exhausted;
		default:
			ut_ad(0);
			/* fall through */
		case SEL_RETRY:
			break;
		}

		plan_reset_cursor(plan);

		mtr.commit();
		mtr.start();
	}
#endif /* BTR_CUR_HASH_ADAPT */

	if (!plan->pcur_is_open) {
		/* Evaluate the expressions to build the search tuple and
		open the cursor */
		err = row_sel_open_pcur(plan, &mtr);

		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			goto mtr_commit_exit;
		}

		cursor_just_opened = TRUE;

		/* A new search was made: increment the cost counter */
		cost_counter++;
	} else {
		/* Restore pcur position to the index */

		must_go_to_next = row_sel_restore_pcur_pos(plan, &mtr);

		cursor_just_opened = FALSE;

		if (must_go_to_next) {
			/* We have already processed the cursor record: move
			to the next */

			goto next_rec;
		}
	}

	if (!node->read_view
	    || trx->isolation_level == TRX_ISO_READ_UNCOMMITTED) {
	} else if (trx_id_t bulk_trx_id = index->table->bulk_trx_id) {
		/* See row_search_mvcc() for a comment on bulk_trx_id */
		if (!trx->read_view.changes_visible(bulk_trx_id)) {
			goto table_exhausted;
		}
	}

rec_loop:
	/* RECORD LOOP
	-----------
	In this loop we use pcur and try to fetch a qualifying row, and
	also fill the prefetch buffer for this table if n_rows_fetched has
	exceeded a threshold. While we are inside this loop, the following
	holds:
	(1) &mtr is started,
	(2) pcur is positioned and open.

	NOTE that if cursor_just_opened is TRUE here, it means that we came
	to this point right after row_sel_open_pcur. */

	ut_ad(mtr_has_extra_clust_latch == FALSE);

	rec = btr_pcur_get_rec(&(plan->pcur));

	/* PHASE 1: Set a lock if specified */

	if (!node->asc && cursor_just_opened
	    && !page_rec_is_supremum(rec)) {

		/* Do not support "descending search" for Spatial index */
		ut_ad(!dict_index_is_spatial(index));

		/* When we open a cursor for a descending search, we must set
		a next-key lock on the successor record: otherwise it would
		be possible to insert new records next to the cursor position,
		and it might be that these new records should appear in the
		search result set, resulting in the phantom problem. */

		if (!node->read_view) {
			const rec_t* next_rec = page_rec_get_next_const(rec);
			if (UNIV_UNLIKELY(!next_rec)) {
				err = DB_CORRUPTION;
				goto lock_wait_or_error;
			}
			unsigned lock_type;

			offsets = rec_get_offsets(next_rec, index, offsets,
						  index->n_core_fields,
						  ULINT_UNDEFINED, &heap);

			/* At READ UNCOMMITTED or READ COMMITTED
			isolation level, we lock only the record,
			i.e., next-key locking is not used. */
			if (trx->isolation_level <= TRX_ISO_READ_COMMITTED) {
				if (page_rec_is_supremum(next_rec)) {
					goto skip_lock;
				}

				lock_type = LOCK_REC_NOT_GAP;
			} else {
				lock_type = LOCK_ORDINARY;
			}

			err = sel_set_rec_lock(&plan->pcur,
					       next_rec, index, offsets,
					       node->row_lock_mode,
					       lock_type, thr, &mtr);

			switch (err) {
			case DB_SUCCESS_LOCKED_REC:
				err = DB_SUCCESS;
				/* fall through */
			case DB_SUCCESS:
				break;
			default:
				/* Note that in this case we will store in pcur
				the PREDECESSOR of the record we are waiting
				the lock for */
				goto lock_wait_or_error;
			}
		}
	}

skip_lock:
	if (page_rec_is_infimum(rec)) {

		/* The infimum record on a page cannot be in the result set,
		and neither can a record lock be placed on it: we skip such
		a record. We also increment the cost counter as we may have
		processed yet another page of index. */

		cost_counter++;

		goto next_rec;
	}

	if (rec_is_metadata(rec, *index)) {
		/* Skip the metadata pseudo-record. */
		cost_counter++;
		goto next_rec;
	}

	if (!node->read_view) {
		/* Try to place a lock on the index record */
		unsigned lock_type;

		offsets = rec_get_offsets(rec, index, offsets,
					  index->n_core_fields,
					  ULINT_UNDEFINED, &heap);

		/* At READ UNCOMMITTED or READ COMMITTED isolation level,
		we lock only the record, i.e., next-key locking is
		not used. */
		if (trx->isolation_level <= TRX_ISO_READ_COMMITTED
		    || dict_index_is_spatial(index)) {

			if (page_rec_is_supremum(rec)) {

				goto next_rec;
			}

			lock_type = LOCK_REC_NOT_GAP;
		} else {
			lock_type = LOCK_ORDINARY;
		}

		err = sel_set_rec_lock(&plan->pcur,
				       rec, index, offsets,
				       node->row_lock_mode, lock_type,
				       thr, &mtr);

		switch (err) {
		case DB_SUCCESS_LOCKED_REC:
			err = DB_SUCCESS;
			/* fall through */
		case DB_SUCCESS:
			break;
		default:
			goto lock_wait_or_error;
		}
	}

	if (page_rec_is_supremum(rec)) {

		/* A page supremum record cannot be in the result set: skip
		it now when we have placed a possible lock on it */

		goto next_rec;
	}

	ut_ad(page_rec_is_user_rec(rec));

	if (cost_counter > SEL_COST_LIMIT) {

		/* Now that we have placed the necessary locks, we can stop
		for a while and store the cursor position; NOTE that if we
		would store the cursor position BEFORE placing a record lock,
		it might happen that the cursor would jump over some records
		that another transaction could meanwhile insert adjacent to
		the cursor: this would result in the phantom problem. */

		goto stop_for_a_while;
	}

	/* PHASE 2: Check a mixed index mix id if needed */

	if (plan->unique_search && cursor_just_opened) {

		ut_ad(plan->mode == PAGE_CUR_GE);

		/* As the cursor is now placed on a user record after a search
		with the mode PAGE_CUR_GE, the up_match field in the cursor
		tells how many fields in the user record matched to the search
		tuple */

		if (btr_pcur_get_up_match(&(plan->pcur))
		    < plan->n_exact_match) {
			goto table_exhausted;
		}

		/* Ok, no need to test end_conds or mix id */

	}

	/* We are ready to look at a possible new index entry in the result
	set: the cursor is now placed on a user record */

	/* PHASE 3: Get previous version in a consistent read */

	cons_read_requires_clust_rec = FALSE;
	offsets = rec_get_offsets(rec, index, offsets, index->n_core_fields,
				  ULINT_UNDEFINED, &heap);

	if (node->read_view) {
		/* This is a non-locking consistent read: if necessary, fetch
		a previous version of the record */

		if (dict_index_is_clust(index)) {
			const trx_id_t id = row_get_rec_trx_id(
				rec, index, offsets);

			if (!node->read_view->changes_visible(id)) {
				if (id >= node->read_view->low_limit_id()
				    && id >= trx_sys.get_max_trx_id()) {
					err = DB_CORRUPTION;
					goto lock_wait_or_error;
				}

				err = row_sel_build_prev_vers(
					node->read_view, index, rec,
					&offsets, &heap, &plan->old_vers_heap,
					&old_vers, &mtr);

				if (err != DB_SUCCESS) {

					goto lock_wait_or_error;
				}

				if (old_vers == NULL) {
					/* The record does not exist
					in our read view. Skip it, but
					first attempt to determine
					whether the index segment we
					are searching through has been
					exhausted. */

					offsets = rec_get_offsets(
						rec, index, offsets,
						index->n_core_fields,
						ULINT_UNDEFINED, &heap);

					/* Fetch the columns needed in
					test conditions. The clustered
					index record is protected by a
					page latch that was acquired
					by row_sel_open_pcur() or
					row_sel_restore_pcur_pos().
					The latch will not be released
					until mtr.commit(). */

					row_sel_fetch_columns(
						index, rec, offsets,
						UT_LIST_GET_FIRST(
							plan->columns));

					if (!row_sel_test_end_conds(plan)) {

						goto table_exhausted;
					}

					goto next_rec;
				}

				rec = old_vers;
			}
		} else if (!srv_read_only_mode) {
			trx_id_t trx_id = page_get_max_trx_id(
				btr_pcur_get_page(&plan->pcur));
			ut_ad(trx_id);
			if (!node->read_view->sees(trx_id)) {
				cons_read_requires_clust_rec = TRUE;
			}
		}
	}

	/* PHASE 4: Test search end conditions and deleted flag */

	/* Fetch the columns needed in test conditions.  The record is
	protected by a page latch that was acquired by
	row_sel_open_pcur() or row_sel_restore_pcur_pos().  The latch
	will not be released until mtr.commit(). */

	row_sel_fetch_columns(index, rec, offsets,
			      UT_LIST_GET_FIRST(plan->columns));

	/* Test the selection end conditions: these can only contain columns
	which already are found in the index, even though the index might be
	non-clustered */

	if (plan->unique_search && cursor_just_opened) {

		/* No test necessary: the test was already made above */

	} else if (!row_sel_test_end_conds(plan)) {

		goto table_exhausted;
	}

	if (rec_get_deleted_flag(rec, dict_table_is_comp(plan->table))
	    && !cons_read_requires_clust_rec) {

		/* The record is delete marked: we can skip it if this is
		not a consistent read which might see an earlier version
		of a non-clustered index record */

		if (plan->unique_search) {

			goto table_exhausted;
		}

		goto next_rec;
	}

	/* PHASE 5: Get the clustered index record, if needed and if we did
	not do the search using the clustered index */

	if (plan->must_get_clust || cons_read_requires_clust_rec) {

		/* It was a non-clustered index and we must fetch also the
		clustered index record */

		err = row_sel_get_clust_rec(node, plan, rec, thr, &clust_rec,
					    &mtr);
		mtr_has_extra_clust_latch = TRUE;

		if (err != DB_SUCCESS) {

			goto lock_wait_or_error;
		}

		/* Retrieving the clustered record required a search:
		increment the cost counter */

		cost_counter++;

		if (clust_rec == NULL) {
			/* The record did not exist in the read view */
			ut_ad(node->read_view);

			goto next_rec;
		}

		if (rec_get_deleted_flag(clust_rec,
					 dict_table_is_comp(plan->table))) {
			/* In delete-marked records, DB_TRX_ID must
			always refer to an existing update_undo log record. */
			ut_ad(rec_get_trx_id(clust_rec,
					     dict_table_get_first_index(
						     plan->table)));

			/* The record is delete marked: we can skip it */

			goto next_rec;
		}

		if (node->can_get_updated) {

			btr_pcur_store_position(&(plan->clust_pcur), &mtr);
		}
	}

	/* PHASE 6: Test the rest of search conditions */

	if (!row_sel_test_other_conds(plan)) {

		if (plan->unique_search) {

			goto table_exhausted;
		}

		goto next_rec;
	}

	/* PHASE 7: We found a new qualifying row for the current table; push
	the row if prefetch is on, or move to the next table in the join */

	plan->n_rows_fetched++;

	ut_ad(plan->pcur.latch_mode == BTR_SEARCH_LEAF);

	if ((plan->n_rows_fetched <= SEL_PREFETCH_LIMIT)
	    || plan->unique_search || plan->no_prefetch) {

		/* No prefetch in operation: go to the next table */

		goto next_table;
	}

	sel_enqueue_prefetched_row(plan);

	if (plan->n_rows_prefetched == SEL_MAX_N_PREFETCH) {

		/* The prefetch buffer is now full */

		sel_dequeue_prefetched_row(plan);

		goto next_table;
	}

next_rec:
	if (mtr_has_extra_clust_latch) {

		/* We must commit &mtr if we are moving to the next
		non-clustered index record, because we could break the
		latching order if we would access a different clustered
		index page right away without releasing the previous. */

		goto commit_mtr_for_a_while;
	}

	if (node->asc) {
		moved = btr_pcur_move_to_next(&(plan->pcur), &mtr);
	} else {
		moved = btr_pcur_move_to_prev(&(plan->pcur), &mtr);
	}

	if (!moved) {

		goto table_exhausted;
	}

	cursor_just_opened = FALSE;

	/* END OF RECORD LOOP
	------------------ */
	goto rec_loop;

next_table:
	/* We found a record which satisfies the conditions: we can move to
	the next table or return a row in the result set */

	ut_ad(btr_pcur_is_on_user_rec(&plan->pcur));

	if (plan->unique_search && !node->can_get_updated) {

		plan->cursor_at_end = TRUE;
	} else {
		plan->stored_cursor_rec_processed = TRUE;

		btr_pcur_store_position(&(plan->pcur), &mtr);
	}

	mtr.commit();

	mtr_has_extra_clust_latch = FALSE;

next_table_no_mtr:
	/* If we use 'goto' to this label, it means that the row was popped
	from the prefetched rows stack, and &mtr is already committed */

	if (node->fetch_table + 1 == node->n_tables) {

		sel_eval_select_list(node);

		if (node->is_aggregate) {

			goto table_loop;
		}

		sel_assign_into_var_values(node->into_list, node);

		thr->run_node = que_node_get_parent(node);

		err = DB_SUCCESS;
		goto func_exit;
	}

	node->fetch_table++;

	/* When we move to the next table, we first reset the plan cursor:
	we do not care about resetting it when we backtrack from a table */

	plan_reset_cursor(sel_node_get_nth_plan(node, node->fetch_table));

	goto table_loop;

table_exhausted:
	/* The table cursor pcur reached the result set end: backtrack to the
	previous table in the join if we do not have cached prefetched rows */

	plan->cursor_at_end = TRUE;

	mtr.commit();

	mtr_has_extra_clust_latch = FALSE;

	if (plan->n_rows_prefetched > 0) {
		/* The table became exhausted during a prefetch */

		sel_dequeue_prefetched_row(plan);

		goto next_table_no_mtr;
	}

table_exhausted_no_mtr:
	if (node->fetch_table == 0) {
		err = DB_SUCCESS;

		if (node->is_aggregate && !node->aggregate_already_fetched) {

			node->aggregate_already_fetched = TRUE;

			sel_assign_into_var_values(node->into_list, node);

			thr->run_node = que_node_get_parent(node);
		} else {
			node->state = SEL_NODE_NO_MORE_ROWS;

			thr->run_node = que_node_get_parent(node);
		}

		goto func_exit;
	}

	node->fetch_table--;

	goto table_loop;

stop_for_a_while:
	/* Return control for a while to que_run_threads, so that runaway
	queries can be canceled. NOTE that when we come here, we must, in a
	locking read, have placed the necessary (possibly waiting request)
	record lock on the cursor record or its successor: when we reposition
	the cursor, this record lock guarantees that nobody can meanwhile have
	inserted new records which should have appeared in the result set,
	which would result in the phantom problem. */

	plan->stored_cursor_rec_processed = FALSE;
	btr_pcur_store_position(&(plan->pcur), &mtr);

	err = DB_SUCCESS;
	goto mtr_commit_exit;

commit_mtr_for_a_while:
	/* Stores the cursor position and commits &mtr; this is used if
	&mtr may contain latches which would break the latching order if
	&mtr would not be committed and the latches released. */

	plan->stored_cursor_rec_processed = TRUE;

	btr_pcur_store_position(&(plan->pcur), &mtr);

	mtr.commit();

	mtr_has_extra_clust_latch = FALSE;

	goto table_loop;

lock_wait_or_error:
	/* See the note at stop_for_a_while: the same holds for this case */

	ut_ad(!btr_pcur_is_before_first_on_page(&plan->pcur) || !node->asc);

	plan->stored_cursor_rec_processed = FALSE;
	btr_pcur_store_position(&(plan->pcur), &mtr);
mtr_commit_exit:
	mtr.commit();

func_exit:
	if (heap != NULL) {
		mem_heap_free(heap);
	}
	return(err);
}

/**********************************************************************//**
Performs a select step. This is a high-level function used in SQL execution
graphs.
@return query thread to run next or NULL */
que_thr_t*
row_sel_step(
/*=========*/
	que_thr_t*	thr)	/*!< in: query thread */
{
	sel_node_t*	node;

	ut_ad(thr);

	node = static_cast<sel_node_t*>(thr->run_node);

	ut_ad(que_node_get_type(node) == QUE_NODE_SELECT);

	/* If this is a new time this node is executed (or when execution
	resumes after wait for a table intention lock), set intention locks
	on the tables, or assign a read view */

	if (node->into_list && (thr->prev_node == que_node_get_parent(node))) {

		node->state = SEL_NODE_OPEN;
	}

	if (node->state == SEL_NODE_OPEN) {

		/* It may be that the current session has not yet started
		its transaction, or it has been committed: */

		trx_start_if_not_started_xa(thr_get_trx(thr), false);

		plan_reset_cursor(sel_node_get_nth_plan(node, 0));

		if (node->consistent_read) {
			trx_t *trx = thr_get_trx(thr);
			/* Assign a read view for the query */
			trx->read_view.open(trx);
			node->read_view = trx->read_view.is_open() ?
					  &trx->read_view : NULL;
		} else {
			sym_node_t*	table_node;
			lock_mode	i_lock_mode;

			if (node->set_x_locks) {
				i_lock_mode = LOCK_IX;
			} else {
				i_lock_mode = LOCK_IS;
			}

			for (table_node = node->table_list;
			     table_node != 0;
			     table_node = static_cast<sym_node_t*>(
					que_node_get_next(table_node))) {

				dberr_t	err = lock_table(
					table_node->table, nullptr,
					i_lock_mode, thr);

				if (err != DB_SUCCESS) {
					trx_t*	trx;

					trx = thr_get_trx(thr);
					trx->error_state = err;

					return(NULL);
				}
			}
		}

		/* If this is an explicit cursor, copy stored procedure
		variable values, so that the values cannot change between
		fetches (currently, we copy them also for non-explicit
		cursors) */

		if (node->explicit_cursor
		    && UT_LIST_GET_FIRST(node->copy_variables)) {

			row_sel_copy_input_variable_vals(node);
		}

		node->state = SEL_NODE_FETCH;
		node->fetch_table = 0;

		if (node->is_aggregate) {
			/* Reset the aggregate total values */
			sel_reset_aggregate_vals(node);
		}
	}

	dberr_t	err = row_sel(node, thr);

	/* NOTE! if queries are parallelized, the following assignment may
	have problems; the assignment should be made only if thr is the
	only top-level thr in the graph: */

	thr->graph->last_sel_node = node;

	if (err != DB_SUCCESS) {
		thr_get_trx(thr)->error_state = err;

		return(NULL);
	}

	return(thr);
}

/**********************************************************************//**
Performs a fetch for a cursor.
@return query thread to run next or NULL */
que_thr_t*
fetch_step(
/*=======*/
	que_thr_t*	thr)	/*!< in: query thread */
{
	sel_node_t*	sel_node;
	fetch_node_t*	node;

	ut_ad(thr);

	node = static_cast<fetch_node_t*>(thr->run_node);
	sel_node = node->cursor_def;

	ut_ad(que_node_get_type(node) == QUE_NODE_FETCH);

	if (thr->prev_node != que_node_get_parent(node)) {

		if (sel_node->state != SEL_NODE_NO_MORE_ROWS) {

			if (node->into_list) {
				sel_assign_into_var_values(node->into_list,
							   sel_node);
			} else {
				ibool ret = (*node->func->func)(
					sel_node, node->func->arg);

				if (!ret) {
					sel_node->state
						 = SEL_NODE_NO_MORE_ROWS;
				}
			}
		}

		thr->run_node = que_node_get_parent(node);

		return(thr);
	}

	/* Make the fetch node the parent of the cursor definition for
	the time of the fetch, so that execution knows to return to this
	fetch node after a row has been selected or we know that there is
	no row left */

	sel_node->common.parent = node;

	if (sel_node->state == SEL_NODE_CLOSED) {
		ib::error() << "fetch called on a closed cursor";

		thr_get_trx(thr)->error_state = DB_ERROR;

		return(NULL);
	}

	thr->run_node = sel_node;

	return(thr);
}

/***********************************************************//**
Prints a row in a select result.
@return query thread to run next or NULL */
que_thr_t*
row_printf_step(
/*============*/
	que_thr_t*	thr)	/*!< in: query thread */
{
	row_printf_node_t*	node;
	sel_node_t*		sel_node;
	que_node_t*		arg;

	ut_ad(thr);

	node = static_cast<row_printf_node_t*>(thr->run_node);

	sel_node = node->sel_node;

	ut_ad(que_node_get_type(node) == QUE_NODE_ROW_PRINTF);

	if (thr->prev_node == que_node_get_parent(node)) {

		/* Reset the cursor */
		sel_node->state = SEL_NODE_OPEN;

		/* Fetch next row to print */

		thr->run_node = sel_node;

		return(thr);
	}

	if (sel_node->state != SEL_NODE_FETCH) {

		ut_ad(sel_node->state == SEL_NODE_NO_MORE_ROWS);

		/* No more rows to print */

		thr->run_node = que_node_get_parent(node);

		return(thr);
	}

	arg = sel_node->select_list;

	while (arg) {
		dfield_print_also_hex(que_node_get_val(arg));

		fputs(" ::: ", stderr);

		arg = que_node_get_next(arg);
	}

	putc('\n', stderr);

	/* Fetch next row to print */

	thr->run_node = sel_node;

	return(thr);
}

/****************************************************************//**
Converts a key value stored in MySQL format to an Innobase dtuple. The last
field of the key value may be just a prefix of a fixed length field: hence
the parameter key_len. But currently we do not allow search keys where the
last field is only a prefix of the full key field len and print a warning if
such appears. A counterpart of this function is
ha_innobase::store_key_val_for_row() in ha_innodb.cc. */
void
row_sel_convert_mysql_key_to_innobase(
/*==================================*/
	dtuple_t*	tuple,		/*!< in/out: tuple where to build;
					NOTE: we assume that the type info
					in the tuple is already according
					to index! */
	byte*		buf,		/*!< in: buffer to use in field
					conversions; NOTE that dtuple->data
					may end up pointing inside buf so
					do not discard that buffer while
					the tuple is being used. See
					row_mysql_store_col_in_innobase_format()
					in the case of DATA_INT */
	ulint		buf_len,	/*!< in: buffer length */
	dict_index_t*	index,		/*!< in: index of the key value */
	const byte*	key_ptr,	/*!< in: MySQL key value */
	ulint		key_len)	/*!< in: MySQL key value length */
{
	byte*		original_buf	= buf;
	const byte*	original_key_ptr = key_ptr;
	dict_field_t*	field;
	dfield_t*	dfield;
	ulint		data_offset;
	ulint		data_len;
	ulint		data_field_len;
	ibool		is_null;
	const byte*	key_end;
	ulint		n_fields = 0;

	/* For documentation of the key value storage format in MySQL, see
	ha_innobase::store_key_val_for_row() in ha_innodb.cc. */

	key_end = key_ptr + key_len;

	/* Permit us to access any field in the tuple: */

	ut_d(dtuple_set_n_fields(tuple, uint16_t(~0)));

	dfield = dtuple_get_nth_field(tuple, 0);
	field = dict_index_get_nth_field(index, 0);

	if (UNIV_UNLIKELY(dfield_get_type(dfield)->mtype == DATA_SYS)) {
		/* A special case: we are looking for a position in the
		generated clustered index which InnoDB automatically added
		to a table with no primary key: the first and the only
		ordering column is ROW_ID which InnoDB stored to the key_ptr
		buffer. */

		ut_a(key_len == DATA_ROW_ID_LEN);

		dfield_set_data(dfield, key_ptr, DATA_ROW_ID_LEN);

		dtuple_set_n_fields(tuple, 1);

		return;
	}

	while (key_ptr < key_end) {

		ulint	type = dfield_get_type(dfield)->mtype;
		ut_a(field->col->mtype == type);

		data_offset = 0;
		is_null = FALSE;

		if (!(dfield_get_type(dfield)->prtype & DATA_NOT_NULL)) {
			/* The first byte in the field tells if this is
			an SQL NULL value */

			data_offset = 1;

			if (*key_ptr != 0) {
				dfield_set_null(dfield);

				is_null = TRUE;
			}
		}

		/* Calculate data length and data field total length */
		if (DATA_LARGE_MTYPE(type) || DATA_GEOMETRY_MTYPE(type)) {

			/* For R-tree index, data length should be the
			total size of the wkb data.*/
			if (dict_index_is_spatial(index)) {
				ut_ad(DATA_GEOMETRY_MTYPE(type));
				data_len = key_len;
				data_field_len = data_offset + data_len;
			} else {
				/* The key field is a column prefix of a BLOB
				or TEXT. */

				ut_a(field->prefix_len > 0);

				/* MySQL stores the actual data length to the
				first 2 bytes after the optional SQL NULL
				marker byte. The storage format is
				little-endian, that is, the most significant
				byte at a higher address. In UTF-8, MySQL
				seems to reserve field->prefix_len bytes for
				storing this field in the key value buffer,
				even though the actual value only takes data
				len bytes from the start. */

				data_len = ulint(key_ptr[data_offset])
					| ulint(key_ptr[data_offset + 1]) << 8;
				data_field_len = data_offset + 2
					+ field->prefix_len;

				data_offset += 2;

				/* Now that we know the length, we store the
				column value like it would be a fixed char
				field */
			}


		} else if (field->prefix_len > 0) {
			/* Looks like MySQL pads unused end bytes in the
			prefix with space. Therefore, also in UTF-8, it is ok
			to compare with a prefix containing full prefix_len
			bytes, and no need to take at most prefix_len / 3
			UTF-8 characters from the start.
			If the prefix is used as the upper end of a LIKE
			'abc%' query, then MySQL pads the end with chars
			0xff. TODO: in that case does it any harm to compare
			with the full prefix_len bytes. How do characters
			0xff in UTF-8 behave? */

			data_len = field->prefix_len;
			data_field_len = data_offset + data_len;
		} else {
			data_len = dfield_get_type(dfield)->len;
			data_field_len = data_offset + data_len;
		}

		if ((dtype_get_mysql_type(dfield_get_type(dfield))
		     == DATA_MYSQL_TRUE_VARCHAR)
		    && (type != DATA_INT)) {
			/* In a MySQL key value format, a true VARCHAR is
			always preceded by 2 bytes of a length field.
			dfield_get_type(dfield)->len returns the maximum
			'payload' len in bytes. That does not include the
			2 bytes that tell the actual data length.

			We added the check != DATA_INT to make sure we do
			not treat MySQL ENUM or SET as a true VARCHAR! */

			data_len += 2;
			data_field_len += 2;
		}

		/* Storing may use at most data_len bytes of buf */

		if (UNIV_LIKELY(!is_null)) {
			buf = row_mysql_store_col_in_innobase_format(
					dfield, buf,
					FALSE, /* MySQL key value format col */
					key_ptr + data_offset, data_len,
					dict_table_is_comp(index->table));
			ut_a(buf <= original_buf + buf_len);
		}

		key_ptr += data_field_len;

		if (UNIV_UNLIKELY(key_ptr > key_end)) {
			/* The last field in key was not a complete key field
			but a prefix of it.

			Print a warning about this! HA_READ_PREFIX_LAST does
			not currently work in InnoDB with partial-field key
			value prefixes. Since MySQL currently uses a padding
			trick to calculate LIKE 'abc%' type queries there
			should never be partial-field prefixes in searches. */

			ib::warn() << "Using a partial-field key prefix in"
				" search, index " << index->name
				<< " of table " << index->table->name
				<< ". Last data field length "
				<< data_field_len << " bytes, key ptr now"
				" exceeds key end by " << (key_ptr - key_end)
				<< " bytes. Key value in the MariaDB format:";

			ut_print_buf(stderr, original_key_ptr, key_len);
			putc('\n', stderr);

			if (!is_null) {
				ulint	len = dfield_get_len(dfield);
				dfield_set_len(dfield, len
					       - (ulint) (key_ptr - key_end));
			}
			ut_ad(0);
		}

		n_fields++;
		field++;
		dfield++;
	}

	ut_a(buf <= original_buf + buf_len);

	/* We set the length of tuple to n_fields: we assume that the memory
	area allocated for it is big enough (usually bigger than n_fields). */

	dtuple_set_n_fields(tuple, uint16_t(n_fields));
}

/**************************************************************//**
Stores a non-SQL-NULL field in the MySQL format. The counterpart of this
function is row_mysql_store_col_in_innobase_format() in row0mysql.cc. */
void
row_sel_field_store_in_mysql_format_func(
	byte*		dest,
	const mysql_row_templ_t* templ,
#ifdef UNIV_DEBUG
	const dict_index_t* index,
	ulint		field_no,
#endif /* UNIV_DEBUG */
	const byte*	data,
	ulint		len)
{
#ifdef UNIV_DEBUG
	const dict_field_t*	field
		= templ->is_virtual
			 ? NULL : dict_index_get_nth_field(index, field_no);
#endif /* UNIV_DEBUG */

	ut_ad(len != UNIV_SQL_NULL);
	MEM_CHECK_DEFINED(data, len);
	MEM_CHECK_ADDRESSABLE(dest, templ->mysql_col_len);
	MEM_UNDEFINED(dest, templ->mysql_col_len);

	byte* pad = dest + len;

	switch (templ->type) {
		const byte*	field_end;
	case DATA_VARCHAR:
	case DATA_VARMYSQL:
	case DATA_BINARY:
		field_end = dest + templ->mysql_col_len;

		if (templ->mysql_type == DATA_MYSQL_TRUE_VARCHAR) {
			/* This is a >= 5.0.3 type true VARCHAR. Store the
			length of the data to the first byte or the first
			two bytes of dest. */

			dest = row_mysql_store_true_var_len(
				dest, len, templ->mysql_length_bytes);
			/* Copy the actual data. Leave the rest of the
			buffer uninitialized. */
			memcpy(dest, data, len);
			break;
		}

		/* Copy the actual data */
		memcpy(dest, data, len);

		/* Pad with trailing spaces. */

		if (pad == field_end) {
			break;
		}

		if (UNIV_UNLIKELY(templ->type == DATA_FIXBINARY)) {
			memset(pad, 0, field_end - pad);
			break;
		}

		ut_ad(templ->mbminlen <= templ->mbmaxlen);

		/* We treat some Unicode charset strings specially. */
		switch (templ->mbminlen) {
		case 4:
			/* InnoDB should never have stripped partial
			UTF-32 characters. */
			ut_a(!(len & 3));
			break;
		case 2:
			/* A space char is two bytes,
			0x0020 in UCS2 and UTF-16 */

			if (UNIV_UNLIKELY(len & 1)) {
				/* A 0x20 has been stripped from the column.
				Pad it back. */

				if (pad < field_end) {
					*pad++ = 0x20;
				}
			}
		}

		row_mysql_pad_col(templ->mbminlen, pad,
				  ulint(field_end - pad));
		break;

	case DATA_BLOB:
		/* Store a pointer to the BLOB buffer to dest: the BLOB was
		already copied to the buffer in row_sel_store_mysql_rec */

		row_mysql_store_blob_ref(dest, templ->mysql_col_len, data,
					 len);
		break;

	case DATA_GEOMETRY:
		/* We store all geometry data as BLOB data at server layer. */
		row_mysql_store_geometry(dest, templ->mysql_col_len, data, len);
		break;

	case DATA_MYSQL:
		memcpy(dest, data, len);

		ut_ad(templ->mysql_col_len >= len);
		ut_ad(templ->mbmaxlen >= templ->mbminlen);

		/* If field_no equals to templ->icp_rec_field_no,
		we are examining a row pointed by "icp_rec_field_no".
		There is possibility that icp_rec_field_no refers to
		a field in a secondary index while templ->rec_field_no
		points to field in a primary index. The length
		should still be equal, unless the field pointed
		by icp_rec_field_no has a prefix */
		ut_ad(templ->mbmaxlen > templ->mbminlen
		      || templ->mysql_col_len == len
		      || (field_no == templ->icp_rec_field_no
			  && field->prefix_len > 0));

		/* The following assertion would fail for old tables
		containing UTF-8 ENUM columns due to Bug #9526. */
		ut_ad(!templ->mbmaxlen
		      || !(templ->mysql_col_len % templ->mbmaxlen));
		ut_ad(len * templ->mbmaxlen >= templ->mysql_col_len
		      || (field_no == templ->icp_rec_field_no
			  && field->prefix_len > 0)
		      || templ->rec_field_is_prefix);

		ut_ad(templ->is_virtual
		      || !(field->prefix_len % templ->mbmaxlen));

		if (templ->mbminlen == 1 && templ->mbmaxlen != 1) {
			/* Pad with spaces. This undoes the stripping
			done in row0mysql.cc, function
			row_mysql_store_col_in_innobase_format(). */

			memset(pad, 0x20, templ->mysql_col_len - len);
		}
		break;

	default:
#ifdef UNIV_DEBUG
	case DATA_SYS_CHILD:
	case DATA_SYS:
		/* These column types should never be shipped to MySQL. */
		ut_ad(0);
		/* fall through */

	case DATA_CHAR:
	case DATA_FIXBINARY:
	case DATA_FLOAT:
	case DATA_DOUBLE:
	case DATA_DECIMAL:
#endif /* UNIV_DEBUG */
		ut_ad((templ->is_virtual && !field)
		      || (field && field->prefix_len
				? field->prefix_len == len
				: templ->mysql_col_len == len));
		memcpy(dest, data, len);
		break;

	case DATA_INT:
		/* Convert InnoDB big-endian integer to little-endian
		format, sign bit restored to 2's complement form */
		DBUG_ASSERT(templ->mysql_col_len == len);

		byte* ptr = pad;
		do *--ptr = *data++; while (ptr != dest);
		if (!templ->is_unsigned) {
			pad[-1] ^= 0x80;
		}
	}
}

/** Convert a field in the Innobase format to a field in the MySQL format.
@param[out]	mysql_rec		record in the MySQL format
@param[in,out]	prebuilt		prebuilt struct
@param[in]	rec			InnoDB record; must be protected
					by a page latch
@param[in]	index			index of rec
@param[in]	offsets			array returned by rec_get_offsets()
@param[in]	field_no		templ->rec_field_no or
					templ->clust_rec_field_no
					or templ->icp_rec_field_no
@param[in]	templ			row template
*/
static MY_ATTRIBUTE((warn_unused_result))
ibool
row_sel_store_mysql_field(
	byte*			mysql_rec,
	row_prebuilt_t*		prebuilt,
	const rec_t*		rec,
	const dict_index_t*	index,
	const rec_offs*		offsets,
	ulint			field_no,
	const mysql_row_templ_t*templ)
{
	DBUG_ENTER("row_sel_store_mysql_field_func");

	const byte*	data;
	ulint		len;

	ut_ad(prebuilt->default_rec);
	ut_ad(templ);
	ut_ad(templ >= prebuilt->mysql_template);
	ut_ad(templ < &prebuilt->mysql_template[prebuilt->n_template]);
	ut_ad(field_no == templ->clust_rec_field_no
	      || field_no == templ->rec_field_no
	      || field_no == templ->icp_rec_field_no);
	ut_ad(rec_offs_validate(rec, index, offsets));

	if (UNIV_UNLIKELY(rec_offs_nth_extern(offsets, field_no) != 0)) {

		mem_heap_t*	heap;
		/* Copy an externally stored field to a temporary heap */

		ut_ad(field_no == templ->clust_rec_field_no);

		if (DATA_LARGE_MTYPE(templ->type)) {
			if (prebuilt->blob_heap == NULL) {
				prebuilt->blob_heap = mem_heap_create(
					srv_page_size);
			}

			heap = prebuilt->blob_heap;
		} else {
			heap = mem_heap_create(srv_page_size);
		}

		/* NOTE: if we are retrieving a big BLOB, we may
		already run out of memory in the next call, which
		causes an assert */

		data = btr_rec_copy_externally_stored_field(
			rec, offsets, prebuilt->table->space->zip_size(),
			field_no, &len, heap);

		if (UNIV_UNLIKELY(!data)) {
			/* The externally stored field was not written
			yet. This record should only be seen by
			trx_rollback_recovered() or any
			TRX_ISO_READ_UNCOMMITTED transactions. */

			if (heap != prebuilt->blob_heap) {
				mem_heap_free(heap);
			}

			ut_a(prebuilt->trx->isolation_level
			     == TRX_ISO_READ_UNCOMMITTED);
			DBUG_RETURN(FALSE);
		}

		ut_a(len != UNIV_SQL_NULL);

		row_sel_field_store_in_mysql_format(
			mysql_rec + templ->mysql_col_offset,
			templ, index, field_no, data, len);

		if (heap != prebuilt->blob_heap) {
			mem_heap_free(heap);
		}
	} else {
		/* The field is stored in the index record, or
		in the metadata for instant ADD COLUMN. */
		data = rec_get_nth_cfield(rec, index, offsets, field_no, &len);

		if (len == UNIV_SQL_NULL) {
			/* MySQL assumes that the field for an SQL
			NULL value is set to the default value. */
			ut_ad(templ->mysql_null_bit_mask);

			MEM_CHECK_DEFINED(prebuilt->default_rec
					  + templ->mysql_col_offset,
					  templ->mysql_col_len);
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wconversion" /* GCC 5 may need this here */
#endif
			mysql_rec[templ->mysql_null_byte_offset]
				|= (byte) templ->mysql_null_bit_mask;
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic pop
#endif
			memcpy(mysql_rec + templ->mysql_col_offset,
			       (const byte*) prebuilt->default_rec
			       + templ->mysql_col_offset,
			       templ->mysql_col_len);
			DBUG_RETURN(TRUE);
		}

		if (DATA_LARGE_MTYPE(templ->type)
		    || DATA_GEOMETRY_MTYPE(templ->type)) {

			/* It is a BLOB field locally stored in the
			InnoDB record: we MUST copy its contents to
			prebuilt->blob_heap here because
			row_sel_field_store_in_mysql_format() stores a
			pointer to the data, and the data passed to us
			will be invalid as soon as the
			mini-transaction is committed and the page
			latch on the clustered index page is
			released. */

			if (prebuilt->blob_heap == NULL) {
				prebuilt->blob_heap = mem_heap_create(
					srv_page_size);
				DBUG_PRINT("anna", ("blob_heap allocated: %p",
						    prebuilt->blob_heap));
			}

			data = static_cast<byte*>(
				mem_heap_dup(prebuilt->blob_heap, data, len));
		}

		row_sel_field_store_in_mysql_format(
			mysql_rec + templ->mysql_col_offset,
			templ, index, field_no, data, len);
	}

	ut_ad(len != UNIV_SQL_NULL);

	if (templ->mysql_null_bit_mask) {
		/* It is a nullable column with a non-NULL
		value */
		mysql_rec[templ->mysql_null_byte_offset]
			&= static_cast<byte>(~templ->mysql_null_bit_mask);
	}

	DBUG_RETURN(TRUE);
}

/** Convert a row in the Innobase format to a row in the MySQL format.
Note that the template in prebuilt may advise us to copy only a few
columns to mysql_rec, other columns are left blank. All columns may not
be needed in the query.
@param[out]	mysql_rec	row in the MySQL format
@param[in]	prebuilt	cursor
@param[in]	rec		Innobase record in the index
				which was described in prebuilt's
				template, or in the clustered index;
				must be protected by a page latch
@param[in]	vrow		virtual columns
@param[in]	rec_clust	whether index must be the clustered index
@param[in]	index		index of rec
@param[in]	offsets		array returned by rec_get_offsets(rec)
@retval true on success
@retval false if not all columns could be retrieved */
MY_ATTRIBUTE((warn_unused_result))
static bool row_sel_store_mysql_rec(
	byte*		mysql_rec,
	row_prebuilt_t*	prebuilt,
	const rec_t*	rec,
	const dtuple_t*	vrow,
	bool		rec_clust,
	const dict_index_t* index,
	const rec_offs*	offsets)
{
	DBUG_ENTER("row_sel_store_mysql_rec");

	ut_ad(rec_clust || index == prebuilt->index);
	ut_ad(!rec_clust || dict_index_is_clust(index));

	/* Secondary index reads populate only templated columns.
	Seed the NULL bitmap from default_rec so uncovered columns
	read as SQL NULL in ha_partition::swap_blobs(). */
	if (!dict_index_is_clust(index) &&
	    prebuilt->m_mysql_table &&
	    prebuilt->m_mysql_table->s->blob_fields &&
	    prebuilt->null_bitmap_len) {
		ut_ad(prebuilt->default_rec);
		memcpy(mysql_rec, prebuilt->default_rec,
		       prebuilt->null_bitmap_len);
	}

	if (UNIV_LIKELY_NULL(prebuilt->blob_heap)) {
		row_mysql_prebuilt_free_blob_heap(prebuilt);
	}

	for (ulint i = 0; i < prebuilt->n_template; i++) {
		const mysql_row_templ_t*templ = &prebuilt->mysql_template[i];

		if (templ->is_virtual && dict_index_is_clust(index)) {
			/* Skip virtual columns if it is not a covered
			search or virtual key read is not requested. */
			if (!rec_clust
			    || !prebuilt->index->has_virtual()
			    || !prebuilt->read_just_key) {
				/* Initialize the NULL bit. */
				if (templ->mysql_null_bit_mask) {
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wconversion" /* GCC 5 may need this here */
#endif
					mysql_rec[templ->mysql_null_byte_offset]
						|= (byte) templ->mysql_null_bit_mask;
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic pop
#endif
				}
				continue;
			}

			dict_v_col_t*   col;
			col = dict_table_get_nth_v_col(
				index->table, templ->clust_rec_field_no);

			ut_ad(vrow);

			const dfield_t* dfield = dtuple_get_nth_v_field(
				vrow, col->v_pos);

			if (dfield_get_type(dfield)->mtype == DATA_MISSING) {
				ut_ad("no ha_innopart in MariaDB" == 0);
				continue;
			}

			if (dfield->len == UNIV_SQL_NULL) {
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wconversion" /* GCC 5 may need this here */
#endif
				mysql_rec[templ->mysql_null_byte_offset]
				|= (byte) templ->mysql_null_bit_mask;
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic pop
#endif
				memcpy(mysql_rec
				+ templ->mysql_col_offset,
				(const byte*) prebuilt->default_rec
				+ templ->mysql_col_offset,
				templ->mysql_col_len);
			} else {
				row_sel_field_store_in_mysql_format(
				mysql_rec + templ->mysql_col_offset,
				templ, index, templ->clust_rec_field_no,
				(const byte*)dfield->data, dfield->len);
				if (templ->mysql_null_bit_mask) {
					mysql_rec[
						templ->mysql_null_byte_offset]
						&= static_cast<byte>
						(~templ->mysql_null_bit_mask);
				}
			}

			continue;
		}

		const ulint		field_no
			= rec_clust
			? templ->clust_rec_field_no
			: templ->rec_field_no;
		/* We should never deliver column prefixes to the SQL layer,
		except for evaluating handler_index_cond_check()
		or handler_rowid_filter_check(). */
		/* ...actually, we do want to do this in order to
		support the prefix query optimization.

		ut_ad(dict_index_get_nth_field(index, field_no)->prefix_len
		      == 0);

		...so we disable this assert. */

		if (!row_sel_store_mysql_field(mysql_rec, prebuilt,
					       rec, index, offsets,
					       field_no, templ)) {

			DBUG_RETURN(false);
		}
	}

	/* FIXME: We only need to read the doc_id if an FTS indexed
	column is being updated.
	NOTE, the record can be cluster or secondary index record.
	if secondary index is used then FTS_DOC_ID column should be part
	of this index. */
	if (dict_table_has_fts_index(prebuilt->table)) {
		if (dict_index_is_clust(index)
		    || prebuilt->fts_doc_id_in_read_set) {
			prebuilt->fts_doc_id = fts_get_doc_id_from_rec(
				rec, index, offsets);
		}
	}

	DBUG_RETURN(true);
}

static void row_sel_reset_old_vers_heap(row_prebuilt_t *prebuilt)
{
  if (prebuilt->old_vers_heap)
    mem_heap_empty(prebuilt->old_vers_heap);
  else
    prebuilt->old_vers_heap= mem_heap_create(200);
}

/*********************************************************************//**
Builds a previous version of a clustered index record for a consistent read
@return DB_SUCCESS or error code */
static MY_ATTRIBUTE((warn_unused_result))
dberr_t
row_sel_build_prev_vers_for_mysql(
/*==============================*/
	row_prebuilt_t*	prebuilt,	/*!< in/out: prebuilt struct */
	dict_index_t*	clust_index,	/*!< in: clustered index */
	const rec_t*	rec,		/*!< in: record in a clustered index */
	rec_offs**	offsets,	/*!< in/out: offsets returned by
					rec_get_offsets(rec, clust_index) */
	mem_heap_t**	offset_heap,	/*!< in/out: memory heap from which
					the offsets are allocated */
	rec_t**		old_vers,	/*!< out: old version, or NULL if the
					record does not exist in the view:
					i.e., it was freshly inserted
					afterwards */
	dtuple_t**	vrow,		/*!< out: dtuple to hold old virtual
					column data */
	mtr_t*		mtr)		/*!< in: mtr */
{
	row_sel_reset_old_vers_heap(prebuilt);

	return row_vers_build_for_consistent_read(
		rec, mtr, clust_index, offsets,
		&prebuilt->trx->read_view, offset_heap,
		prebuilt->old_vers_heap, old_vers, vrow);
}

/** Helper class to cache clust_rec and old_vers */
class Row_sel_get_clust_rec_for_mysql
{
  const rec_t *cached_clust_rec;
  rec_t *cached_old_vers;
  lsn_t cached_lsn;
  page_id_t cached_page_id;

#ifdef UNIV_DEBUG
  void check_eq(const dict_index_t *index, const rec_offs *offsets) const
  {
    rec_offs vers_offs[REC_OFFS_HEADER_SIZE + MAX_REF_PARTS];
    rec_offs_init(vers_offs);
    mem_heap_t *heap= nullptr;

    ut_ad(rec_offs_validate(cached_clust_rec, index, offsets));
    ut_ad(index->first_user_field() <= rec_offs_n_fields(offsets));
    ut_ad(vers_offs == rec_get_offsets(cached_old_vers, index, vers_offs,
                                       index->n_core_fields,
                                       index->db_trx_id(), &heap));
    ut_ad(!heap);
    for (auto n= index->db_trx_id(); n--; )
    {
      const dict_col_t *col= dict_index_get_nth_col(index, n);
      ulint len1, len2;
      const byte *b1= rec_get_nth_field(cached_clust_rec, offsets, n, &len1);
      const byte *b2= rec_get_nth_field(cached_old_vers, vers_offs, n, &len2);
      ut_ad(!cmp_data(col->mtype, col->prtype, false, b1, len1, b2, len2));
    }
  }
#endif

public:
  Row_sel_get_clust_rec_for_mysql() :
    cached_clust_rec(NULL), cached_old_vers(NULL), cached_lsn(0),
    cached_page_id(page_id_t(0,0)) {}

  dberr_t operator()(row_prebuilt_t *prebuilt, dict_index_t *sec_index,
                     const rec_t *rec, que_thr_t *thr, const rec_t **out_rec,
                     rec_offs **offsets, mem_heap_t **offset_heap,
                     dtuple_t **vrow, mtr_t *mtr);
};

/*********************************************************************//**
Retrieves the clustered index record corresponding to a record in a
non-clustered index. Does the necessary locking. Used in the MySQL
interface.
@return DB_SUCCESS, DB_SUCCESS_LOCKED_REC, or error code */
dberr_t
Row_sel_get_clust_rec_for_mysql::operator()(
/*============================*/
	row_prebuilt_t*	prebuilt,/*!< in: prebuilt struct in the handle */
	dict_index_t*	sec_index,/*!< in: secondary index where rec resides */
	const rec_t*	rec,	/*!< in: record in a non-clustered index; if
				this is a locking read, then rec is not
				allowed to be delete-marked, and that would
				not make sense either */
	que_thr_t*	thr,	/*!< in: query thread */
	const rec_t**	out_rec,/*!< out: clustered record or an old version of
				it, NULL if the old version did not exist
				in the read view, i.e., it was a fresh
				inserted version */
	rec_offs**	offsets,/*!< in: offsets returned by
				rec_get_offsets(rec, sec_index);
				out: offsets returned by
				rec_get_offsets(out_rec, clust_index) */
	mem_heap_t**	offset_heap,/*!< in/out: memory heap from which
				the offsets are allocated */
	dtuple_t**	vrow,	/*!< out: virtual column to fill */
	mtr_t*		mtr)	/*!< in: mtr used to get access to the
				non-clustered record; the same mtr is used to
				access the clustered index */
{
	dict_index_t*	clust_index;
	rec_t*		old_vers;
	trx_t*		trx;

	prebuilt->clust_pcur->old_rec = nullptr;
	*out_rec = NULL;
	trx = thr_get_trx(thr);

	row_build_row_ref_in_tuple(prebuilt->clust_ref, rec,
				   sec_index, *offsets);

	clust_index = dict_table_get_first_index(sec_index->table);
	prebuilt->clust_pcur->btr_cur.page_cur.index = clust_index;

	dberr_t err = btr_pcur_open_with_no_init(prebuilt->clust_ref,
						 PAGE_CUR_LE, BTR_SEARCH_LEAF,
						 prebuilt->clust_pcur, mtr);
	if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
		return err;
	}

	const rec_t* clust_rec = btr_pcur_get_rec(prebuilt->clust_pcur);

	prebuilt->clust_pcur->trx_if_known = trx;

	/* Note: only if the search ends up on a non-infimum record is the
	low_match value the real match to the search tuple */

	if (!page_rec_is_user_rec(clust_rec)
	    || btr_pcur_get_low_match(prebuilt->clust_pcur)
	    < dict_index_get_n_unique(clust_index)) {
		btr_cur_t*	btr_cur = btr_pcur_get_btr_cur(prebuilt->pcur);

		/* If this is a spatial index scan, and we are reading
		from a shadow buffer, the record could be already
		deleted (due to rollback etc.). So get the original
		page and verify that */
		if  (dict_index_is_spatial(sec_index)
		     && btr_cur->rtr_info->matches
		     && (!(ulint(rec
				 - btr_cur->rtr_info->matches->block->page.frame)
			   >> srv_page_size_shift)
			|| rec != btr_pcur_get_rec(prebuilt->pcur))) {
#ifdef UNIV_DEBUG
			rtr_info_t*	rtr_info = btr_cur->rtr_info;
			mysql_mutex_lock(&rtr_info->matches->rtr_match_mutex);
			/* The page could be deallocated (by rollback etc.) */
			if (!rtr_info->matches->valid) {
				mysql_mutex_unlock(&rtr_info->matches->rtr_match_mutex);
				clust_rec = NULL;
                                goto func_exit;
			}
			mysql_mutex_unlock(&rtr_info->matches->rtr_match_mutex);

			if (rec_get_deleted_flag(rec,
                                          dict_table_is_comp(sec_index->table))
                                  && prebuilt->select_lock_type == LOCK_NONE) {

				clust_rec = NULL;
				goto func_exit;
			}

			if (rec != btr_pcur_get_rec(prebuilt->pcur)) {
				clust_rec = NULL;
                                goto func_exit;
			}

			/* FIXME: Why is this block not the
			same as btr_pcur_get_block(prebuilt->pcur),
			and is it not unsafe to use RW_NO_LATCH here? */
			buf_block_t*	block = buf_page_get_gen(
				btr_pcur_get_block(prebuilt->pcur)->page.id(),
				btr_pcur_get_block(prebuilt->pcur)->zip_size(),
				RW_NO_LATCH, NULL, BUF_GET, mtr, &err);
			ut_ad(block); // FIXME: avoid crash
			mem_heap_t*	heap = mem_heap_create(256);
			dtuple_t*       tuple = dict_index_build_data_tuple(
				rec, sec_index, true,
				sec_index->n_fields, heap);
			page_cur_t     page_cursor;
			page_cursor.block = block;
			page_cursor.index = sec_index;
			uint16_t up_match = 0, low_match = 0;
			ut_ad(!page_cur_search_with_match(tuple, PAGE_CUR_LE,
							  &up_match,
							  &low_match,
							  &page_cursor,
							  nullptr));
			ut_ad(low_match < dtuple_get_n_fields_cmp(tuple));
			mem_heap_free(heap);
			err = DB_SUCCESS;
#endif /* UNIV_DEBUG */
		} else if (!rec_get_deleted_flag(rec,
					  dict_table_is_comp(sec_index->table))
			   || prebuilt->select_lock_type != LOCK_NONE) {
			/* In a rare case it is possible that no clust
			rec is found for a delete-marked secondary index
			record: if row_undo_mod_clust() has already removed
			the clust rec, while purge is still cleaning and
			removing secondary index records associated with
			earlier versions of the clustered index record.
			In that case we know that the clustered index
			record did not exist in the read view of trx. */
			ib::error() << "Clustered record for sec rec not found"
				" index " << sec_index->name
				<< " of table " << sec_index->table->name;

			fputs("InnoDB: sec index record ", stderr);
			rec_print(stderr, rec, sec_index);
			fputs("\n"
			      "InnoDB: clust index record ", stderr);
			rec_print(stderr, clust_rec, clust_index);
			err = DB_CORRUPTION;
		}

		clust_rec = NULL;
		goto func_exit;
	}

	*offsets = rec_get_offsets(clust_rec, clust_index, *offsets,
				   clust_index->n_core_fields,
				   ULINT_UNDEFINED, offset_heap);

	if (prebuilt->select_lock_type != LOCK_NONE) {
		/* Try to place a lock on the index record; we are searching
		the clust rec with a unique condition, hence
		we set a LOCK_REC_NOT_GAP type lock */

		err = lock_clust_rec_read_check_and_lock(
			0, btr_pcur_get_block(prebuilt->clust_pcur),
			clust_rec, clust_index, *offsets,
			prebuilt->select_lock_type,
			LOCK_REC_NOT_GAP,
			thr);

		switch (err) {
		case DB_SUCCESS:
		case DB_SUCCESS_LOCKED_REC:
			break;
		default:
			return err;
		}
	} else {
		/* This is a non-locking consistent read: if necessary, fetch
		a previous version of the record */

		old_vers = NULL;

		if (trx->isolation_level == TRX_ISO_READ_UNCOMMITTED
		    || clust_index->table->is_temporary()) {
		} else {
			/* If the isolation level allows reading of
			uncommitted data, then we never look for an
			earlier version */
			err = row_sel_clust_sees(clust_rec, *clust_index,
						 *offsets, trx->read_view);
		}

		switch (err) {
		default:
			return err;
		case DB_SUCCESS:
			break;
		case DB_SUCCESS_LOCKED_REC:
			const buf_page_t& bpage = btr_pcur_get_block(
				prebuilt->clust_pcur)->page;

			const lsn_t lsn = mach_read_from_8(
				bpage.frame + FIL_PAGE_LSN);

			if (lsn != cached_lsn
			    || bpage.id() != cached_page_id
			    || clust_rec != cached_clust_rec) {
				/* The following call returns 'offsets' associated with
				'old_vers' */
				err = row_sel_build_prev_vers_for_mysql(
					prebuilt, clust_index,
					clust_rec, offsets, offset_heap, &old_vers,
					vrow, mtr);

				if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
					return err;
				}
				cached_lsn = lsn;
				cached_page_id = bpage.id();
				cached_clust_rec = clust_rec;
				cached_old_vers = old_vers;
			} else {
				err = DB_SUCCESS;
				old_vers = cached_old_vers;

				/* The offsets need not be same for the latest
				version of clust_rec and its old version
				old_vers. Re-calculate the offsets for old_vers. */

				if (old_vers) {
					ut_d(check_eq(clust_index, *offsets));
					*offsets = rec_get_offsets(
						old_vers, clust_index, *offsets,
						clust_index->n_core_fields,
						ULINT_UNDEFINED, offset_heap);
				}
			}

			if (old_vers == NULL) {
				return err;
			}

			clust_rec = old_vers;
		}

		/* If we had to go to an earlier version of row or the
		secondary index record is delete marked, then it may be that
		the secondary index record corresponding to clust_rec
		(or old_vers) is not rec; in that case we must ignore
		such row because in our snapshot rec would not have existed.
		Remember that from rec we cannot see directly which transaction
		id corresponds to it: we have to go to the clustered index
		record. A query where we want to fetch all rows where
		the secondary index value is in some interval would return
		a wrong result if we would not drop rows which we come to
		visit through secondary index records that would not really
		exist in our snapshot. */

		/* And for spatial index, since the rec is from shadow buffer,
		so we need to check if it's exactly match the clust_rec. */
		if (clust_rec
		    && (old_vers
			|| trx->isolation_level <= TRX_ISO_READ_UNCOMMITTED
			|| dict_index_is_spatial(sec_index)
			|| rec_get_deleted_flag(rec, dict_table_is_comp(
							sec_index->table)))) {
			err = row_sel_sec_rec_is_for_clust_rec(rec, sec_index,
						clust_rec, clust_index, thr);
			switch (err) {
			case DB_SUCCESS:
				clust_rec = NULL;
				break;
			case DB_SUCCESS_LOCKED_REC:
				break;
			default:
				return err;
			}
		}

		err = DB_SUCCESS;
	}

func_exit:
	*out_rec = clust_rec;

	if (prebuilt->select_lock_type != LOCK_NONE) {
		/* We may use the cursor in update or in unlock_row():
		store its position */

		btr_pcur_store_position(prebuilt->clust_pcur, mtr);
	}

	return err;
}

/** Restores cursor position after it has been stored. We have to take into
account that the record cursor was positioned on may have been deleted.
Then we may have to move the cursor one step up or down.
@param[out] same_user_rec true if we were able to restore the cursor on a user
record with the same ordering prefix in in the B-tree index
@param[in] latch_mode latch mode wished in restoration
@param[in] pcur cursor whose position has been stored
@param[in] moves_up true if the cursor moves up in the index
@param[in,out] mtr mtr; CAUTION: may commit mtr temporarily!
@return true if we may need to process the record the cursor is now
positioned on (i.e. we should not go to the next record yet) */
static bool sel_restore_position_for_mysql(bool *same_user_rec,
                                           btr_latch_mode latch_mode,
                                           btr_pcur_t *pcur,
                                           bool moves_up, mtr_t *mtr)
{
	auto status = pcur->restore_position(latch_mode, mtr);

	*same_user_rec = status == btr_pcur_t::SAME_ALL;

	ut_ad(!*same_user_rec || pcur->rel_pos == BTR_PCUR_ON);
#ifdef UNIV_DEBUG
	if (pcur->pos_state == BTR_PCUR_IS_POSITIONED_OPTIMISTIC) {
		ut_ad(pcur->rel_pos == BTR_PCUR_BEFORE
		      || pcur->rel_pos == BTR_PCUR_AFTER);
	} else {
		ut_ad(pcur->pos_state == BTR_PCUR_IS_POSITIONED);
		ut_ad((pcur->rel_pos == BTR_PCUR_ON)
		      == btr_pcur_is_on_user_rec(pcur));
	}
#endif /* UNIV_DEBUG */

	/* The position may need be adjusted for rel_pos and moves_up. */

	switch (pcur->rel_pos) {
	case BTR_PCUR_ON:
		if (!*same_user_rec && moves_up) {
			if (status == btr_pcur_t::SAME_UNIQ)
			  return true;
next:
			if (btr_pcur_move_to_next(pcur, mtr)
			    && rec_is_metadata(btr_pcur_get_rec(pcur),
					       *pcur->index())) {
				btr_pcur_move_to_next(pcur, mtr);
			}

			return true;
		}
		return(!*same_user_rec);
	case BTR_PCUR_AFTER_LAST_IN_TREE:
	case BTR_PCUR_BEFORE_FIRST_IN_TREE:
		return true;
	case BTR_PCUR_AFTER:
		/* positioned to record after pcur->old_rec. */
		pcur->pos_state = BTR_PCUR_IS_POSITIONED;
prev:
		if (btr_pcur_is_on_user_rec(pcur) && !moves_up
		    && !rec_is_metadata(btr_pcur_get_rec(pcur),
					*pcur->index())) {
			if (!btr_pcur_move_to_prev(pcur, mtr)) {
				return true;
			}
		}
		return true;
	case BTR_PCUR_BEFORE:
		/* For non optimistic restoration:
		The position is now set to the record before pcur->old_rec.

		For optimistic restoration:
		The position also needs to take the previous search_mode into
		consideration. */

		switch (pcur->pos_state) {
		case BTR_PCUR_IS_POSITIONED_OPTIMISTIC:
			pcur->pos_state = BTR_PCUR_IS_POSITIONED;
			if (pcur->search_mode == PAGE_CUR_GE) {
				/* Positioned during Greater or Equal search
				with BTR_PCUR_BEFORE. Optimistic restore to
				the same record. If scanning for lower then
				we must move to previous record.
				This can happen with:
				HANDLER READ idx a = (const);
				HANDLER READ idx PREV; */
				goto prev;
			}
			return true;
		case BTR_PCUR_IS_POSITIONED:
			if (moves_up && btr_pcur_is_on_user_rec(pcur)) {
				goto next;
			}
			return true;
		case BTR_PCUR_WAS_POSITIONED:
		case BTR_PCUR_NOT_POSITIONED:
			break;
		}
	}
	ut_ad(0);
	return true;
}

/********************************************************************//**
Copies a cached field for MySQL from the fetch cache. */
static
void
row_sel_copy_cached_field_for_mysql(
/*================================*/
	byte*			buf,	/*!< in/out: row buffer */
	const byte*		cache,	/*!< in: cached row */
	const mysql_row_templ_t*templ)	/*!< in: column template */
{
	ulint	len;

	buf += templ->mysql_col_offset;
	cache += templ->mysql_col_offset;

	MEM_CHECK_ADDRESSABLE(buf, templ->mysql_col_len);

	if (templ->mysql_type == DATA_MYSQL_TRUE_VARCHAR
	    && (templ->type != DATA_INT)) {
		/* Check for != DATA_INT to make sure we do
		not treat MySQL ENUM or SET as a true VARCHAR!
		Find the actual length of the true VARCHAR field. */
		row_mysql_read_true_varchar(
			&len, cache, templ->mysql_length_bytes);
		len += templ->mysql_length_bytes;
		MEM_UNDEFINED(buf, templ->mysql_col_len);
	} else {
		len = templ->mysql_col_len;
	}

	memcpy(buf, cache, len);
}

/** Copy used fields from cached row.
Copy cache record field by field, don't touch fields that
are not covered by current key.
@param[out]	buf		Where to copy the MySQL row.
@param[in]	cached_rec	What to copy (in MySQL row format).
@param[in]	prebuilt	prebuilt struct. */
void
row_sel_copy_cached_fields_for_mysql(
	byte*		buf,
	const byte*	cached_rec,
	row_prebuilt_t*	prebuilt)
{
	const mysql_row_templ_t*templ;
	ulint			i;
	for (i = 0; i < prebuilt->n_template; i++) {
		templ = prebuilt->mysql_template + i;

		/* Skip virtual columns */
		if (templ->is_virtual) {
			continue;
		}

		row_sel_copy_cached_field_for_mysql(
			buf, cached_rec, templ);
		/* Copy NULL bit of the current field from cached_rec
		to buf */
		if (templ->mysql_null_bit_mask) {
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wconversion" /* GCC 5 may need this here */
#endif
			buf[templ->mysql_null_byte_offset]
				^= (buf[templ->mysql_null_byte_offset]
				    ^ cached_rec[templ->mysql_null_byte_offset])
				& (byte) templ->mysql_null_bit_mask;
#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
# pragma GCC diagnostic pop
#endif
		}
	}
}

/********************************************************************//**
Pops a cached row for MySQL from the fetch cache. */
UNIV_INLINE
void
row_sel_dequeue_cached_row_for_mysql(
/*=================================*/
	byte*		buf,		/*!< in/out: buffer where to copy the
					row */
	row_prebuilt_t*	prebuilt)	/*!< in: prebuilt struct */
{
	ulint			i;
	const mysql_row_templ_t*templ;
	const byte*		cached_rec;
	ut_ad(prebuilt->n_fetch_cached > 0);
	ut_ad(prebuilt->mysql_prefix_len <= prebuilt->mysql_row_len);

	MEM_CHECK_ADDRESSABLE(buf, prebuilt->mysql_row_len);

	cached_rec = prebuilt->fetch_cache[prebuilt->fetch_cache_first];

	if (UNIV_UNLIKELY(prebuilt->keep_other_fields_on_keyread)) {
		row_sel_copy_cached_fields_for_mysql(buf, cached_rec, prebuilt);
	} else if (prebuilt->mysql_prefix_len > 63) {
		/* The record is long. Copy it field by field, in case
		there are some long VARCHAR column of which only a
		small length is being used. */
		MEM_UNDEFINED(buf, prebuilt->mysql_prefix_len);

		/* First copy the NULL bits. */
		memcpy(buf, cached_rec, prebuilt->null_bitmap_len);
		/* Then copy the requested fields. */

		for (i = 0; i < prebuilt->n_template; i++) {
			templ = prebuilt->mysql_template + i;

			/* Skip virtual columns */
			if (templ->is_virtual
			    && !(dict_index_has_virtual(prebuilt->index)
				 && prebuilt->read_just_key)) {
				continue;
			}

			row_sel_copy_cached_field_for_mysql(
				buf, cached_rec, templ);
		}
	} else {
		memcpy(buf, cached_rec, prebuilt->mysql_prefix_len);
	}

	prebuilt->n_fetch_cached--;
	prebuilt->fetch_cache_first++;

	if (prebuilt->n_fetch_cached == 0) {
		prebuilt->fetch_cache_first = 0;
	}
}

/********************************************************************//**
Initialise the prefetch cache. */
UNIV_INLINE
void
row_sel_prefetch_cache_init(
/*========================*/
	row_prebuilt_t*	prebuilt)	/*!< in/out: prebuilt struct */
{
	ulint	i;
	ulint	sz;
	byte*	ptr;

	/* Reserve space for the magic number. */
	sz = UT_ARR_SIZE(prebuilt->fetch_cache) * (prebuilt->mysql_row_len + 8);
	ptr = static_cast<byte*>(ut_malloc_nokey(sz));

	for (i = 0; i < UT_ARR_SIZE(prebuilt->fetch_cache); i++) {

		/* A user has reported memory corruption in these
		buffers in Linux. Put magic numbers there to help
		to track a possible bug. */

		mach_write_to_4(ptr, ROW_PREBUILT_FETCH_MAGIC_N);
		ptr += 4;

		prebuilt->fetch_cache[i] = ptr;
		ptr += prebuilt->mysql_row_len;

		mach_write_to_4(ptr, ROW_PREBUILT_FETCH_MAGIC_N);
		ptr += 4;
	}
}

/********************************************************************//**
Get the last fetch cache buffer from the queue.
@return pointer to buffer. */
UNIV_INLINE
byte*
row_sel_fetch_last_buf(
/*===================*/
	row_prebuilt_t*	prebuilt)	/*!< in/out: prebuilt struct */
{
	ut_ad(!prebuilt->templ_contains_blob);
	ut_ad(prebuilt->n_fetch_cached < MYSQL_FETCH_CACHE_SIZE);

	if (prebuilt->fetch_cache[0] == NULL) {
		/* Allocate memory for the fetch cache */
		ut_ad(prebuilt->n_fetch_cached == 0);

		row_sel_prefetch_cache_init(prebuilt);
	}

	ut_ad(prebuilt->fetch_cache_first == 0);
	MEM_UNDEFINED(prebuilt->fetch_cache[prebuilt->n_fetch_cached],
		      prebuilt->mysql_row_len);

	return(prebuilt->fetch_cache[prebuilt->n_fetch_cached]);
}

/********************************************************************//**
Pushes a row for MySQL to the fetch cache. */
UNIV_INLINE
void
row_sel_enqueue_cache_row_for_mysql(
/*================================*/
	byte*		mysql_rec,	/*!< in/out: MySQL record */
	row_prebuilt_t*	prebuilt)	/*!< in/out: prebuilt struct */
{
	/* For non ICP code path the row should already exist in the
	next fetch cache slot. */

	if (prebuilt->pk_filter || prebuilt->idx_cond) {
		memcpy(row_sel_fetch_last_buf(prebuilt), mysql_rec,
		       prebuilt->mysql_row_len);
	}

	++prebuilt->n_fetch_cached;
}

#ifdef BTR_CUR_HASH_ADAPT
/*********************************************************************//**
Tries to do a shortcut to fetch a clustered index record with a unique key,
using the hash index if possible (not always). We assume that the search
mode is PAGE_CUR_GE, it is a consistent read, there is a read view in trx,
btr search latch has been locked in S-mode if AHI is enabled.
@return SEL_FOUND, SEL_EXHAUSTED, SEL_RETRY */
static
ulint
row_sel_try_search_shortcut_for_mysql(
/*==================================*/
	const rec_t**	out_rec,/*!< out: record if found */
	row_prebuilt_t*	prebuilt,/*!< in: prebuilt struct */
	rec_offs**	offsets,/*!< in/out: for rec_get_offsets(*out_rec) */
	mem_heap_t**	heap,	/*!< in/out: heap for rec_get_offsets() */
	mtr_t*		mtr)	/*!< in: started mtr */
{
	dict_index_t*	index		= prebuilt->index;
	const dtuple_t*	search_tuple	= prebuilt->search_tuple;
	btr_pcur_t*	pcur		= prebuilt->pcur;
	trx_t*		trx		= prebuilt->trx;
	const rec_t*	rec;

	ut_ad(index->is_primary());
	ut_ad(!index->table->is_temporary());
	ut_ad(!prebuilt->templ_contains_blob);
	ut_ad(trx->read_view.is_open());
	pcur->old_rec = nullptr;

	if (btr_pcur_open_with_no_init(search_tuple, PAGE_CUR_GE,
				       BTR_SEARCH_LEAF, pcur, mtr)
	    != DB_SUCCESS) {
		return SEL_RETRY;
	}

	rec = btr_pcur_get_rec(pcur);

	if (!page_rec_is_user_rec(rec) || rec_is_metadata(rec, *index)) {
		return SEL_RETRY;
	}

	/* As the cursor is now placed on a user record after a search with
	the mode PAGE_CUR_GE, the up_match field in the cursor tells how many
	fields in the user record matched to the search tuple */

	if (btr_pcur_get_up_match(pcur) < dtuple_get_n_fields(search_tuple)) {
		return SEL_EXHAUSTED;
	}

	if (trx->isolation_level == TRX_ISO_READ_UNCOMMITTED) {
	} else if (trx_id_t bulk_trx_id = index->table->bulk_trx_id) {
		/* See row_search_mvcc() for a comment on bulk_trx_id */
		if (!trx->read_view.changes_visible(bulk_trx_id)) {
			return SEL_EXHAUSTED;
		}
	}

	/* This is a non-locking consistent read: if necessary, fetch
	a previous version of the record */

	*offsets = rec_get_offsets(rec, index, *offsets, index->n_core_fields,
				   ULINT_UNDEFINED, heap);

	if (row_sel_clust_sees(rec, *index, *offsets, trx->read_view)
	    != DB_SUCCESS) {
		return SEL_RETRY;
	}

	if (rec_get_deleted_flag(rec, dict_table_is_comp(index->table))) {
		/* In delete-marked records, DB_TRX_ID must
		always refer to an existing undo log record. */
		ut_ad(row_get_rec_trx_id(rec, index, *offsets));
		return SEL_EXHAUSTED;
	}

	*out_rec = rec;

	return SEL_FOUND;
}
#endif /* BTR_CUR_HASH_ADAPT */

/*********************************************************************//**
Check a pushed-down index condition.
@return CHECK_ABORTED_BY_USER, CHECK_NEG, CHECK_POS, or CHECK_OUT_OF_RANGE */
static
check_result_t
row_search_idx_cond_check(
/*======================*/
	byte*			mysql_rec,	/*!< out: record
						in MySQL format (invalid unless
						prebuilt->idx_cond!=NULL and
						we return CHECK_POS) */
	row_prebuilt_t*		prebuilt,	/*!< in/out: prebuilt struct
						for the table handle */
	const rec_t*		rec,		/*!< in: InnoDB record */
	const rec_offs*		offsets)	/*!< in: rec_get_offsets() */
{
	ulint		i;

	ut_ad(rec_offs_validate(rec, prebuilt->index, offsets));

	if (!prebuilt->idx_cond) {
		if (!prebuilt->pk_filter ||
                    !handler_rowid_filter_is_active(prebuilt->pk_filter)) {
			return(CHECK_POS);
		}
	} else {
		MONITOR_INC(MONITOR_ICP_ATTEMPTS);
	}

	/* Convert to MySQL format those fields that are needed for
	evaluating the index condition. */

	if (UNIV_LIKELY_NULL(prebuilt->blob_heap)) {
		mem_heap_empty(prebuilt->blob_heap);
	}

	for (i = 0; i < prebuilt->idx_cond_n_cols; i++) {
		const mysql_row_templ_t*templ = &prebuilt->mysql_template[i];

		/* Skip virtual columns */
		if (templ->is_virtual) {
			continue;
		}

		if (!row_sel_store_mysql_field(mysql_rec, prebuilt,
					       rec, prebuilt->index, offsets,
					       templ->icp_rec_field_no,
					       templ)) {
			return(CHECK_NEG);
		}
	}

	/* We assume that the index conditions on
	case-insensitive columns are case-insensitive. The
	case of such columns may be wrong in a secondary
	index, if the case of the column has been updated in
	the past, or a record has been deleted and a record
	inserted in a different case. */
	check_result_t result = prebuilt->idx_cond
		? handler_index_cond_check(prebuilt->idx_cond)
		: CHECK_POS;

	switch (result) {
	case CHECK_POS:
	        if (prebuilt->pk_filter &&
                  handler_rowid_filter_is_active(prebuilt->pk_filter)) {
		        ut_ad(!prebuilt->index->is_primary());
		        if (prebuilt->clust_index_was_generated) {
                               ulint len;
                               dict_index_t* index = prebuilt->index;
                               const byte* data = rec_get_nth_field(
                                       rec, offsets, index->n_fields - 1,
                                       &len);
                               ut_ad(dict_index_get_nth_col(index,
                                                            index->n_fields - 1)
                                     ->prtype == (DATA_ROW_ID | DATA_NOT_NULL));
                               ut_ad(len == DATA_ROW_ID_LEN);
                               memcpy(prebuilt->row_id, data, DATA_ROW_ID_LEN);
                        }
                        result = handler_rowid_filter_check(prebuilt->pk_filter);
                        switch (result) {
                        case CHECK_NEG:
			        MONITOR_INC(MONITOR_ICP_NO_MATCH);
                                return(result);
                        case CHECK_OUT_OF_RANGE:
                                MONITOR_INC(MONITOR_ICP_OUT_OF_RANGE);
                                return(result);
                        case CHECK_POS:
                                break;
                        default:
                                return(result);
                        }
		}
		/* Convert the remaining fields to MySQL format.
		If this is a secondary index record, we must defer
		this until we have fetched the clustered index record. */
		if (!prebuilt->need_to_access_clustered
		    || dict_index_is_clust(prebuilt->index)) {
			if (!row_sel_store_mysql_rec(
				    mysql_rec, prebuilt, rec, NULL, false,
				    prebuilt->index, offsets)) {
				ut_ad(dict_index_is_clust(prebuilt->index));
				return(CHECK_NEG);
			}
		}
		MONITOR_INC(MONITOR_ICP_MATCH);
		return(result);
	case CHECK_NEG:
		MONITOR_INC(MONITOR_ICP_NO_MATCH);
		return(result);
	case CHECK_OUT_OF_RANGE:
		MONITOR_INC(MONITOR_ICP_OUT_OF_RANGE);
		return(result);
        case CHECK_ERROR:
        case CHECK_ABORTED_BY_USER:
		return(result);
	}

	ut_error;
	return(result);
}

/** Extract virtual column data from a virtual index record and fill a dtuple
@param[in]	rec		the virtual (secondary) index record
@param[in]	index		the virtual index
@param[in,out]	vrow		the dtuple where data extract to
@param[in]	heap		memory heap to allocate memory
*/
static
void
row_sel_fill_vrow(
	const rec_t*		rec,
	dict_index_t*		index,
	dtuple_t**		vrow,
	mem_heap_t*		heap)
{
	rec_offs offsets_[REC_OFFS_NORMAL_SIZE];
	rec_offs* offsets	= offsets_;
	rec_offs_init(offsets_);

	ut_ad(!(*vrow));
	ut_ad(heap);
	ut_ad(!dict_index_is_clust(index));
	ut_ad(!index->is_instant());
	ut_ad(page_rec_is_leaf(rec));

	offsets = rec_get_offsets(rec, index, offsets, index->n_core_fields,
				  ULINT_UNDEFINED, &heap);

	*vrow = dtuple_create_with_vcol(heap, 0, index->table->n_v_cols);

	/* Initialize all virtual row's mtype to DATA_MISSING */
	dtuple_init_v_fld(*vrow);

	for (ulint i = 0; i < dict_index_get_n_fields(index); i++) {
		const dict_field_t*     field;
		const dict_col_t*       col;

		field = dict_index_get_nth_field(index, i);
		col = dict_field_get_col(field);

		if (col->is_virtual()) {
			const byte*     data;
			ulint           len;

			data = rec_get_nth_field(rec, offsets, i, &len);

			const dict_v_col_t*     vcol = reinterpret_cast<
				const dict_v_col_t*>(col);

			dfield_t* dfield = dtuple_get_nth_v_field(
				*vrow, vcol->v_pos);
			dfield_set_data(dfield, data, len);
			dict_col_copy_type(col, dfield_get_type(dfield));
		}
	}
}

/** Return the record field length in characters.
@param[in]	col		table column of the field
@param[in]	field_no	field number
@param[in]	rec		physical record
@param[in]	offsets		field offsets in the physical record
@return field length in characters. */
static
size_t
rec_field_len_in_chars(
	const dict_col_t*	col,
	const ulint		field_no,
	const rec_t*		rec,
	const rec_offs*		offsets)
{
	const ulint cset = dtype_get_charset_coll(col->prtype);
	const CHARSET_INFO* cs = all_charsets[cset];
	ulint rec_field_len;
	const char* rec_field = reinterpret_cast<const char *>(
		rec_get_nth_field(
			rec, offsets, field_no, &rec_field_len));

	if (UNIV_UNLIKELY(!cs)) {
		ib::warn() << "Missing collation " << cset;
		return SIZE_T_MAX;
	}

	return cs->numchars(rec_field, rec_field + rec_field_len);
}

/** Avoid the clustered index lookup if all the following conditions
are true:
1) all columns are in secondary index
2) all values for columns that are prefix-only indexes are shorter
than the prefix size. This optimization can avoid many IOs for certain schemas.
@return true, to avoid clustered index lookup. */
static
bool row_search_with_covering_prefix(
	row_prebuilt_t*	prebuilt,
	const rec_t*	rec,
	const rec_offs*	offsets)
{
	const dict_index_t*	index = prebuilt->index;
	ut_ad(!dict_index_is_clust(index));

	/* In ha_innobase::build_template() we choose to access the
	whole row when using exclusive row locks or In case of fts
	query, we need to read from clustered index */
	if (prebuilt->select_lock_type == LOCK_X || prebuilt->in_fts_query
	    || !index->is_btree()) {
		return false;
	}

	/** Optimization only applicable if there the number of secondary index
	fields are greater than or equal to number of clustered index fields. */
	if (prebuilt->n_template > index->n_fields) {
		return false;
	}

	/* We can avoid a clustered index lookup if
	all of the following hold:
	(1) all columns are in the secondary index
	(2) all values for columns that are prefix-only
	indexes are shorter than the prefix size
	This optimization can avoid many IOs for certain schemas. */
	for (ulint i = 0; i < prebuilt->n_template; i++) {
		mysql_row_templ_t* templ = prebuilt->mysql_template + i;
		ulint j = templ->rec_prefix_field_no;
		ut_ad(!templ->mbminlen == !templ->mbmaxlen);

		/** Condition (1) : is the field in the index. */
		if (j == ULINT_UNDEFINED) {
			return false;
		}

		/** Condition (2): If this is a prefix index then
		row's value size shorter than prefix length. */

		if (!templ->rec_field_is_prefix
		    || rec_offs_nth_sql_null(offsets, j)) {
			continue;
		}

		const dict_field_t* field = dict_index_get_nth_field(index, j);

		if (!field->prefix_len) {
			continue;
		}

		const ulint rec_size = rec_offs_nth_size(offsets, j);

		if (rec_size >= field->prefix_len) {
			/* Shortest representation string by the
			byte length of the record is longer than the
			maximum possible index prefix. */
			return false;
		}

		if (templ->mbminlen != templ->mbmaxlen
		    && rec_field_len_in_chars(field->col, j, rec, offsets)
		    >= field->prefix_len / templ->mbmaxlen) {
			/* No of chars to store the record exceeds
			the index prefix character length. */
			return false;
		}
	}

	/* If prefix index optimization condition satisfied then
	for all columns above, use rec_prefix_field_no instead of
	rec_field_no, and skip the clustered lookup below. */
	for (ulint i = 0; i < prebuilt->n_template; i++) {
		mysql_row_templ_t* templ = prebuilt->mysql_template + i;
		templ->rec_field_no = templ->rec_prefix_field_no;
		ut_a(templ->rec_field_no != ULINT_UNDEFINED);
	}

	return true;
}

/** Searches for rows in the database using cursor.
Function is mainly used for tables that are shared across connections and
so it employs technique that can help re-construct the rows that
transaction is suppose to see.
It also has optimization such as pre-caching the rows, using AHI, etc.

@param[out]	buf		buffer for the fetched row in MySQL format
@param[in]	mode		search mode PAGE_CUR_L
@param[in,out]	prebuilt	prebuilt struct for the table handler;
				this contains the info to search_tuple,
				index; if search tuple contains 0 field then
				we position the cursor at start or the end of
				index, depending on 'mode'
@param[in]	match_mode	0 or ROW_SEL_EXACT or ROW_SEL_EXACT_PREFIX
@param[in]	direction	0 or ROW_SEL_NEXT or ROW_SEL_PREV;
				Note: if this is != 0, then prebuilt must has a
				pcur with stored position! In opening of a
				cursor 'direction' should be 0.
@return DB_SUCCESS or error code */
dberr_t
row_search_mvcc(
	byte*		buf,
	page_cur_mode_t	mode,
	row_prebuilt_t*	prebuilt,
	ulint		match_mode,
	ulint		direction)
{
	DBUG_ENTER("row_search_mvcc");
	DBUG_ASSERT(prebuilt->index->table == prebuilt->table);

	dict_index_t*	index		= prebuilt->index;
	ibool		comp		= dict_table_is_comp(prebuilt->table);
	const dtuple_t*	search_tuple	= prebuilt->search_tuple;
	btr_pcur_t*	pcur		= prebuilt->pcur;
	trx_t*		trx		= prebuilt->trx;
	dict_index_t*	clust_index;
	que_thr_t*	thr;
	const rec_t*	UNINIT_VAR(rec);
	dtuple_t*	vrow = NULL;
	const rec_t*	result_rec = NULL;
	const rec_t*	clust_rec;
	Row_sel_get_clust_rec_for_mysql row_sel_get_clust_rec_for_mysql;
	ibool		unique_search			= FALSE;
	ulint		mtr_extra_clust_savepoint	= 0;
	bool		moves_up			= false;
	/* if the returned record was locked and we did a semi-consistent
	read (fetch the newest committed version), then this is set to
	TRUE */
	ulint		next_offs;
	bool		same_user_rec;
	ibool		table_lock_waited		= FALSE;
	byte*		next_buf			= 0;
	bool		spatial_search			= false;

	ut_ad(index && pcur && search_tuple);
	ut_a(prebuilt->magic_n == ROW_PREBUILT_ALLOCATED);
	ut_a(prebuilt->magic_n2 == ROW_PREBUILT_ALLOCATED);

	/* We don't support FTS queries from the HANDLER interfaces, because
	we implemented FTS as reversed inverted index with auxiliary tables.
	So anything related to traditional index query would not apply to
	it. */
	if (prebuilt->index->type & DICT_FTS) {
		DBUG_RETURN(DB_END_OF_INDEX);
	}

	if (!prebuilt->table->space) {
		DBUG_RETURN(DB_TABLESPACE_DELETED);
	} else if (!prebuilt->table->is_readable()) {
		if (fil_space_crypt_t* crypt_data =
		    prebuilt->table->space->crypt_data) {
			if (crypt_data->should_encrypt()) {
				DBUG_RETURN(DB_DECRYPTION_FAILED);
			}
		}
		DBUG_RETURN(DB_CORRUPTION);
	} else if (!prebuilt->index_usable) {
		DBUG_RETURN(DB_MISSING_HISTORY);
	} else if (prebuilt->index->is_corrupted()) {
		DBUG_RETURN(DB_CORRUPTION);
	}

	pcur->btr_cur.page_cur.index = index;

	/* We need to get the virtual column values stored in secondary
	index key, if this is covered index scan or virtual key read is
	requested. */
	bool    need_vrow = prebuilt->read_just_key
		&& prebuilt->index->has_virtual();

	/* Reset the new record lock info if READ UNCOMMITTED or
	READ COMMITED isolation level is used. Then
	we are able to remove the record locks set here on an individual
	row. */
	prebuilt->new_rec_locks = 0;

	/*-------------------------------------------------------------*/
	/* PHASE 1: Try to pop the row from the prefetch cache */

	if (UNIV_UNLIKELY(direction == 0)) {
		trx->op_info = "starting index read";

		prebuilt->n_rows_fetched = 0;
		prebuilt->n_fetch_cached = 0;
		prebuilt->fetch_cache_first = 0;

		if (prebuilt->sel_graph == NULL) {
			/* Build a dummy select query graph */
			row_prebuild_sel_graph(prebuilt);
		}
	} else {
		trx->op_info = "fetching rows";

		if (prebuilt->n_rows_fetched == 0) {
			prebuilt->fetch_direction = direction;
		}

		if (UNIV_UNLIKELY(direction != prebuilt->fetch_direction)) {
			if (UNIV_UNLIKELY(prebuilt->n_fetch_cached > 0)) {
				ut_error;
				/* TODO: scrollable cursor: restore cursor to
				the place of the latest returned row,
				or better: prevent caching for a scroll
				cursor! */
			}

			prebuilt->n_rows_fetched = 0;
			prebuilt->n_fetch_cached = 0;
			prebuilt->fetch_cache_first = 0;

		} else if (UNIV_LIKELY(prebuilt->n_fetch_cached > 0)) {
			row_sel_dequeue_cached_row_for_mysql(buf, prebuilt);

			prebuilt->n_rows_fetched++;
			trx->op_info = "";
			DBUG_RETURN(DB_SUCCESS);
		}

		if (prebuilt->fetch_cache_first > 0
		    && prebuilt->fetch_cache_first < MYSQL_FETCH_CACHE_SIZE) {
early_not_found:
			/* The previous returned row was popped from the fetch
			cache, but the cache was not full at the time of the
			popping: no more rows can exist in the result set */
			trx->op_info = "";
			DBUG_RETURN(DB_RECORD_NOT_FOUND);
		}

#if SIZEOF_SIZE_T < 8
		if (UNIV_LIKELY(~prebuilt->n_rows_fetched))
#endif
		prebuilt->n_rows_fetched++;

		mode = pcur->search_mode;
	}

	/* In a search where at most one record in the index may match, we
	can use a LOCK_REC_NOT_GAP type record lock when locking a
	non-delete-marked matching record.

	Note that in a unique secondary index there may be different
	delete-marked versions of a record where only the primary key
	values differ: thus in a secondary index we must use next-key
	locks when locking delete-marked records. */

	if (match_mode == ROW_SEL_EXACT
	    && dict_index_is_unique(index)
	    && dtuple_get_n_fields(search_tuple)
	    == dict_index_get_n_unique(index)
	    && (dict_index_is_clust(index)
		|| !dtuple_contains_null(search_tuple))) {

		/* Note above that a UNIQUE secondary index can contain many
		rows with the same key value if one of the columns is the SQL
		null. A clustered index under MySQL can never contain null
		columns because we demand that all the columns in primary key
		are non-null. */

		unique_search = TRUE;

		/* Even if the condition is unique, MySQL seems to try to
		retrieve also a second row if a primary key contains more than
		1 column. Return immediately if this is not a HANDLER
		command. */

		if (UNIV_UNLIKELY(direction != 0
				  && !prebuilt->used_in_HANDLER)) {
			goto early_not_found;
		}
	}

	/* We don't support sequential scan for Rtree index because it
	is pointless. */
	if (dict_index_is_spatial(index) && !RTREE_SEARCH_MODE(mode)) {
		trx->op_info = "";
		DBUG_RETURN(DB_END_OF_INDEX);
	}

	/* if the query is a plain locking SELECT, and the isolation level
	is <= TRX_ISO_READ_COMMITTED, then this is set to FALSE */
	bool did_semi_consistent_read = false;
	mtr_t mtr{trx};
	mtr.start();

	mem_heap_t*	heap				= NULL;
	rec_offs	offsets_[REC_OFFS_NORMAL_SIZE];
	rec_offs*	offsets				= offsets_;
	rec_offs_init(offsets_);

#ifdef BTR_CUR_HASH_ADAPT
	/*-------------------------------------------------------------*/
	/* PHASE 2: Try fast adaptive hash index search if possible */

	/* Next test if this is the special case where we can use the fast
	adaptive hash index to try the search. Since we must release the
	search system latch when we retrieve an externally stored field, we
	cannot use the adaptive hash index in a search in the case the row
	may be long and there may be externally stored fields */

	if (UNIV_UNLIKELY(direction == 0)
	    && unique_search
	    && btr_search.enabled
	    && dict_index_is_clust(index)
	    && !index->table->is_temporary()
	    && !prebuilt->templ_contains_blob
	    && !prebuilt->used_in_HANDLER
	    && (prebuilt->mysql_row_len < srv_page_size / 8)) {

		mode = PAGE_CUR_GE;

		if (prebuilt->select_lock_type == LOCK_NONE
		    && trx->isolation_level > TRX_ISO_READ_UNCOMMITTED
		    && trx->read_view.is_open()) {

			/* This is a SELECT query done as a consistent read,
			and the read view has already been allocated:
			let us try a search shortcut through the hash
			index. */

			dberr_t err = DB_SUCCESS;
			switch (row_sel_try_search_shortcut_for_mysql(
					&rec, prebuilt, &offsets, &heap,
					&mtr)) {
			case SEL_FOUND:
				/* At this point, rec is protected by
				a page latch that was acquired by
				row_sel_try_search_shortcut_for_mysql().
				The latch will not be released until
				mtr.commit(). */
				ut_ad(!rec_get_deleted_flag(rec, comp));

				if (prebuilt->pk_filter || prebuilt->idx_cond) {
					switch (row_search_idx_cond_check(
							buf, prebuilt,
							rec, offsets)) {
					case CHECK_ABORTED_BY_USER:
						goto aborted;
					case CHECK_NEG:
					case CHECK_OUT_OF_RANGE:
                                        case CHECK_ERROR:
						err = DB_RECORD_NOT_FOUND;
						goto shortcut_done;
					case CHECK_POS:
						goto shortcut_done;
					}

					ut_ad("incorrect code" == 0);
aborted:
					err = DB_INTERRUPTED;
					goto shortcut_done;
				}

				if (!row_sel_store_mysql_rec(
					    buf, prebuilt,
					    rec, NULL, false, index,
					    offsets)) {
					/* Only fresh inserts may contain
					incomplete externally stored
					columns. Pretend that such
					records do not exist. Such
					records may only be accessed
					at the READ UNCOMMITTED
					isolation level or when
					rolling back a recovered
					transaction. Rollback happens
					at a lower level, not here. */

					/* Proceed as in case SEL_RETRY. */
					break;
				}

				goto shortcut_done;

			case SEL_EXHAUSTED:
				err = DB_RECORD_NOT_FOUND;
			shortcut_done:
				mtr.commit();

				/* NOTE that we do NOT store the cursor
				position */
				trx->op_info = "";
				ut_ad(!did_semi_consistent_read);
				if (UNIV_LIKELY_NULL(heap)) {
					mem_heap_free(heap);
				}
				DBUG_RETURN(err);

			case SEL_RETRY:
				break;

			default:
				ut_ad(0);
			}

			mtr.commit();
			mtr.start();
		}
	}
#endif /* BTR_CUR_HASH_ADAPT */

	/*-------------------------------------------------------------*/
	/* PHASE 3: Open or restore index cursor position */

	spatial_search = dict_index_is_spatial(index)
			 && mode >= PAGE_CUR_CONTAIN;

#ifdef UNIV_DEBUG
	/* The state of a running trx can only be changed by the
	thread that is currently serving the transaction. Because we
	are that thread, we can read trx->state without holding any
	mutex. */
	switch (trx->state) {
	case TRX_STATE_ACTIVE:
		break;
	case TRX_STATE_NOT_STARTED:
		ut_ad(prebuilt->sql_stat_start
		      || prebuilt->table->no_rollback());
		break;
	default:
		ut_ad("invalid trx->state" == 0);
	}
#endif

	ut_ad(prebuilt->sql_stat_start
	      || prebuilt->select_lock_type != LOCK_NONE
	      || trx->read_view.is_open()
	      || prebuilt->table->no_rollback()
	      || srv_read_only_mode);

	/* Do not lock gaps at READ UNCOMMITTED or READ COMMITTED
	isolation level */
	const bool set_also_gap_locks =
		prebuilt->select_lock_type != LOCK_NONE
		&& trx->isolation_level > TRX_ISO_READ_COMMITTED
#ifdef WITH_WSREP
		&& !wsrep_thd_skip_locking(trx->mysql_thd)
#endif /* WITH_WSREP */
		;

	/* Note that if the search mode was GE or G, then the cursor
	naturally moves upward (in fetch next) in alphabetical order,
	otherwise downward */

	if (UNIV_UNLIKELY(direction == 0)) {
		if (mode == PAGE_CUR_GE || mode == PAGE_CUR_G
		    || mode >= PAGE_CUR_CONTAIN) {
			moves_up = true;
		}
	} else if (direction == ROW_SEL_NEXT) {
		moves_up = true;
	}

	thr = que_fork_get_first_thr(prebuilt->sel_graph);

	clust_index = dict_table_get_first_index(prebuilt->table);

	dberr_t err = DB_SUCCESS;

	/* Do some start-of-statement preparations */

	if (prebuilt->table->no_rollback()) {
		/* NO_ROLLBACK tables do not support MVCC or locking. */
		prebuilt->select_lock_type = LOCK_NONE;
		prebuilt->sql_stat_start = FALSE;
	} else if (!prebuilt->sql_stat_start) {
		/* No need to set an intention lock or assign a read view */
		ut_a(prebuilt->select_lock_type != LOCK_NONE
		     || srv_read_only_mode || trx->read_view.is_open());
	} else {
		prebuilt->sql_stat_start = FALSE;
		trx_start_if_not_started(trx, false);

		if (prebuilt->select_lock_type == LOCK_NONE) {
			trx->read_view.open(trx);
		} else {
wait_table_again:
			err = lock_table(prebuilt->table, nullptr,
					 prebuilt->select_lock_type == LOCK_S
					 ? LOCK_IS : LOCK_IX, thr);

			if (err != DB_SUCCESS) {

				table_lock_waited = TRUE;
				goto lock_table_wait;
			}
		}
	}

	/* Open or restore index cursor position */

	if (UNIV_LIKELY(direction != 0)) {
		if (spatial_search) {
			/* R-Tree access does not need to do
			cursor position and reposition */
			goto next_rec;
		}

		bool	need_to_process = sel_restore_position_for_mysql(
			&same_user_rec, BTR_SEARCH_LEAF,
			pcur, moves_up, &mtr);

		if (UNIV_UNLIKELY(need_to_process)) {
			if (UNIV_UNLIKELY(!btr_pcur_get_rec(pcur))) {
				mtr.commit();
				trx->op_info = "";
				if (UNIV_LIKELY_NULL(heap)) {
					mem_heap_free(heap);
				}
				return DB_CORRUPTION;
			}

			if (UNIV_UNLIKELY(prebuilt->row_read_type
					  == ROW_READ_DID_SEMI_CONSISTENT)) {
				/* We did a semi-consistent read,
				but the record was removed in
				the meantime. */
				prebuilt->row_read_type
					= ROW_READ_TRY_SEMI_CONSISTENT;
			}
		} else if (UNIV_LIKELY(prebuilt->row_read_type
				       != ROW_READ_DID_SEMI_CONSISTENT)) {

			/* The cursor was positioned on the record
			that we returned previously.  If we need
			to repeat a semi-consistent read as a
			pessimistic locking read, the record
			cannot be skipped. */

			goto next_rec_after_check;
		}

	} else if (dtuple_get_n_fields(search_tuple) > 0) {
		pcur->old_rec = nullptr;

		if (index->is_spatial()) {
			if (!prebuilt->rtr_info) {
				prebuilt->rtr_info = rtr_create_rtr_info(
					set_also_gap_locks, true, thr,
					btr_pcur_get_btr_cur(pcur));
				prebuilt->rtr_info->search_tuple = search_tuple;
				prebuilt->rtr_info->search_mode = mode;
				rtr_info_update_btr(btr_pcur_get_btr_cur(pcur),
						    prebuilt->rtr_info);
			} else {
				rtr_info_reinit_in_cursor(
					btr_pcur_get_btr_cur(pcur),
					index, set_also_gap_locks);
				prebuilt->rtr_info->search_tuple = search_tuple;
				prebuilt->rtr_info->search_mode = mode;
			}

			err = rtr_search_leaf(pcur, thr, search_tuple, mode,
					      &mtr);
		} else {
			err = btr_pcur_open_with_no_init(search_tuple, mode,
							 BTR_SEARCH_LEAF,
							 pcur, &mtr);
		}

		if (err != DB_SUCCESS) {
page_corrupted:
			rec = NULL;
			goto page_read_error;
		}

		pcur->trx_if_known = trx;

		rec = btr_pcur_get_rec(pcur);
		ut_ad(page_rec_is_leaf(rec));

		if (!moves_up
		    && set_also_gap_locks
		    && !page_rec_is_supremum(rec)
		    && !dict_index_is_spatial(index)) {

			/* Try to place a gap lock on the next index record
			to prevent phantoms in ORDER BY ... DESC queries */
			const rec_t*	next_rec = page_rec_get_next_const(rec);
			if (UNIV_UNLIKELY(!next_rec)) {
				err = DB_CORRUPTION;
				goto page_corrupted;
			}

			offsets = rec_get_offsets(next_rec, index, offsets,
						  index->n_core_fields,
						  ULINT_UNDEFINED, &heap);
			err = sel_set_rec_lock(pcur,
					       next_rec, index, offsets,
					       prebuilt->select_lock_type,
					       LOCK_GAP, thr, &mtr);

			switch (err) {
			case DB_SUCCESS_LOCKED_REC:
				err = DB_SUCCESS;
				/* fall through */
			case DB_SUCCESS:
				break;
			default:
				goto lock_wait_or_error;
			}
		}
	} else if (mode == PAGE_CUR_G || mode == PAGE_CUR_L) {
		err = pcur->open_leaf(mode == PAGE_CUR_G, index,
				      BTR_SEARCH_LEAF, &mtr);

		if (err != DB_SUCCESS) {
			if (err == DB_DECRYPTION_FAILED) {
				innodb_decryption_failed(trx->mysql_thd,
							 index->table);
			}
			rec = NULL;
			goto page_read_error;
		}
	}

	/* Check if the table is supposed to be empty for our read view.

	If we read bulk_trx_id as an older transaction ID, it is not
	incorrect to check here whether that transaction should be
	visible to us. If bulk_trx_id is not visible to us, the table
	must have been empty at an earlier point of time, also in our
	read view.

	An INSERT would only update bulk_trx_id in
	row_ins_clust_index_entry_low() if the table really was empty
	(everything had been purged), when holding a leaf page latch
	in the clustered index (actually, the root page is the only
	leaf page in that case).

	We are already holding a leaf page latch here, either
	in a secondary index or in a clustered index.

	If we are holding a clustered index page latch, there clearly
	is no potential for race condition with a concurrent INSERT:
	such INSERT would be blocked by us.

	If we are holding a secondary index page latch, then we are
	not directly blocking a concurrent INSERT that might update
	bulk_trx_id to something that does not exist in our read view.
	But, in that case, the entire table (all indexes) must have
	been empty. So, even if our read below missed the update of
	index->table->bulk_trx_id, we can safely proceed to reading
	the empty secondary index page. Our latch will prevent the
	INSERT from proceeding to that page. It will first modify
	the clustered index. Also, we may only look up something in
	the clustered index if the secondary index page is not empty
	to begin with. So, only if the table is corrupted
	(the clustered index is empty but the secondary index is not)
	we could return corrupted results. */
	if (trx->isolation_level == TRX_ISO_READ_UNCOMMITTED
	    || !trx->read_view.is_open()) {
	} else if (trx_id_t bulk_trx_id = index->table->bulk_trx_id) {
		/* InnoDB should allow the transaction to read all
		the rows when InnoDB intends to do any locking
		on the record */
		if (prebuilt->select_lock_type == LOCK_NONE
		    && !trx->read_view.changes_visible(bulk_trx_id)) {
			trx->op_info = "";
			err = DB_END_OF_INDEX;
			goto normal_return;
		}
	}

rec_loop:
	DEBUG_SYNC_C("row_search_rec_loop");
	if (trx_is_interrupted(trx)) {
		if (!spatial_search) {
			btr_pcur_store_position(pcur, &mtr);
		}
		err = DB_INTERRUPTED;
		goto normal_return;
	}

	/*-------------------------------------------------------------*/
	/* PHASE 4: Look for matching records in a loop */

	rec = btr_pcur_get_rec(pcur);

	ut_ad(!!page_rec_is_comp(rec) == comp);
	ut_ad(page_rec_is_leaf(rec));

	if (page_rec_is_infimum(rec)) {

		/* The infimum record on a page cannot be in the result set,
		and neither can a record lock be placed on it: we skip such
		a record. */

		goto next_rec;
	}

	if (page_rec_is_supremum(rec)) {

		if (set_also_gap_locks
		    && !dict_index_is_spatial(index)) {

			/* Try to place a lock on the index record */

			/* If the transaction isolation level is
			READ UNCOMMITTED or READ COMMITTED,
			we do not lock gaps. Supremum record is really
			a gap and therefore we do not set locks there. */

			offsets = rec_get_offsets(rec, index, offsets,
						  index->n_core_fields,
						  ULINT_UNDEFINED, &heap);
			err = sel_set_rec_lock(pcur,
					       rec, index, offsets,
					       prebuilt->select_lock_type,
					       LOCK_ORDINARY, thr, &mtr);

			switch (err) {
			case DB_SUCCESS_LOCKED_REC:
				err = DB_SUCCESS;
				/* fall through */
			case DB_SUCCESS:
				break;
			default:
				goto lock_wait_or_error;
			}
		}

		/* A page supremum record cannot be in the result set: skip
		it now that we have placed a possible lock on it */

		goto next_rec;
	}

	/*-------------------------------------------------------------*/
	/* Do sanity checks in case our cursor has bumped into page
	corruption */

	if (comp) {
		if (rec_get_info_bits(rec, true) & REC_INFO_MIN_REC_FLAG) {
			/* Skip the metadata pseudo-record. */
			ut_ad(index->is_instant());
			goto next_rec;
		}

		next_offs = rec_get_next_offs(rec, TRUE);
		if (UNIV_UNLIKELY(next_offs < PAGE_NEW_SUPREMUM)) {

			goto wrong_offs;
		}
	} else {
		if (rec_get_info_bits(rec, false) & REC_INFO_MIN_REC_FLAG) {
			/* Skip the metadata pseudo-record. */
			ut_ad(index->is_instant());
			goto next_rec;
		}

		next_offs = rec_get_next_offs(rec, FALSE);
		if (UNIV_UNLIKELY(next_offs < PAGE_OLD_SUPREMUM)) {

			goto wrong_offs;
		}
	}

	if (UNIV_UNLIKELY(next_offs >= srv_page_size - PAGE_DIR)) {

wrong_offs:
		if (srv_force_recovery == 0 || moves_up == false) {
			ib::error() << "Rec address "
				<< static_cast<const void*>(rec)
				<< ", buf block fix count "
				<< btr_pcur_get_block(pcur)->page
				.buf_fix_count();

			ib::error() << "Index corruption: rec offs "
				<< rec - btr_pcur_get_page(pcur)
				<< " next offs "
				<< next_offs
				<< btr_pcur_get_block(pcur)->page.id()
				<< ", index " << index->name
				<< " of table " << index->table->name
				<< ". Run CHECK TABLE. You may need to"
				" restore from a backup, or dump + drop +"
				" reimport the table.";
			ut_ad(0);
			err = DB_CORRUPTION;

			goto page_read_error;
		} else {
			/* The user may be dumping a corrupt table. Jump
			over the corruption to recover as much as possible. */

			ib::info() << "Index corruption: rec offs "
				<< rec - btr_pcur_get_page(pcur)
				<< " next offs "
				<< next_offs
				<< btr_pcur_get_block(pcur)->page.id()
				<< ", index " << index->name
				<< " of table " << index->table->name
				<< ". We try to skip the rest of the page.";

			page_cur_set_after_last(btr_pcur_get_block(pcur),
						btr_pcur_get_page_cur(pcur));
			pcur->old_rec = nullptr;
			goto next_rec;
		}
	}
	/*-------------------------------------------------------------*/

	/* Calculate the 'offsets' associated with 'rec' */

	ut_ad(fil_page_index_page_check(btr_pcur_get_page(pcur)));
	ut_ad(btr_page_get_index_id(btr_pcur_get_page(pcur)) == index->id);

	offsets = rec_get_offsets(rec, index, offsets, index->n_core_fields,
				  ULINT_UNDEFINED, &heap);

	if (UNIV_UNLIKELY(srv_force_recovery > 0)) {
		if (!rec_validate(rec, offsets)
		    || !btr_index_rec_validate(pcur->btr_cur.page_cur,
					       index, FALSE)) {

			ib::error() << "Index corruption: rec offs "
				<< rec - btr_pcur_get_page(pcur)
				<< " next offs "
				<< next_offs
				<< btr_pcur_get_block(pcur)->page.id()
				<< ", index " << index->name
				<< " of table " << index->table->name
				<< ". We try to skip the record.";

			goto next_rec;
		}
	}

	/* Note that we cannot trust the up_match value in the cursor at this
	place because we can arrive here after moving the cursor! Thus
	we have to recompare rec and search_tuple to determine if they
	match enough. */

	if (match_mode == ROW_SEL_EXACT) {
		/* Test if the index record matches completely to search_tuple
		in prebuilt: if not, then we return with DB_RECORD_NOT_FOUND */

		/* fputs("Comparing rec and search tuple\n", stderr); */

		if (cmp_dtuple_rec(search_tuple, rec, index, offsets)) {

			if (set_also_gap_locks
			    && !dict_index_is_spatial(index)) {
				err = sel_set_rec_lock(
					pcur,
					rec, index, offsets,
					prebuilt->select_lock_type, LOCK_GAP,
					thr, &mtr);

				switch (err) {
				case DB_SUCCESS_LOCKED_REC:
				case DB_SUCCESS:
					break;
				default:
					goto lock_wait_or_error;
				}
			}

			btr_pcur_store_position(pcur, &mtr);

			/* The found record was not a match, but may be used
			as NEXT record (index_next). Set the relative position
			to BTR_PCUR_BEFORE, to reflect that the position of
			the persistent cursor is before the found/stored row
			(pcur->old_rec). */
			ut_ad(pcur->rel_pos == BTR_PCUR_ON);
			pcur->rel_pos = BTR_PCUR_BEFORE;

			err = DB_RECORD_NOT_FOUND;
			goto normal_return;
		}

	} else if (match_mode == ROW_SEL_EXACT_PREFIX) {

		if (!cmp_dtuple_is_prefix_of_rec(search_tuple, rec,
						 index, offsets)) {

			if (set_also_gap_locks
			    && !dict_index_is_spatial(index)) {
				err = sel_set_rec_lock(
					pcur,
					rec, index, offsets,
					prebuilt->select_lock_type, LOCK_GAP,
					thr, &mtr);

				switch (err) {
				case DB_SUCCESS_LOCKED_REC:
				case DB_SUCCESS:
					break;
				default:
					goto lock_wait_or_error;
				}
			}

			btr_pcur_store_position(pcur, &mtr);

			/* The found record was not a match, but may be used
			as NEXT record (index_next). Set the relative position
			to BTR_PCUR_BEFORE, to reflect that the position of
			the persistent cursor is before the found/stored row
			(pcur->old_rec). */
			ut_ad(pcur->rel_pos == BTR_PCUR_ON);
			pcur->rel_pos = BTR_PCUR_BEFORE;

			err = DB_RECORD_NOT_FOUND;
			goto normal_return;
		}
	}

	/* We are ready to look at a possible new index entry in the result
	set: the cursor is now placed on a user record */

	if (prebuilt->select_lock_type != LOCK_NONE) {
		/* Try to place a lock on the index record; note that delete
		marked records are a special case in a unique search. If there
		is a non-delete marked record, then it is enough to lock its
		existence with LOCK_REC_NOT_GAP. */

		unsigned lock_type;

		if (trx->isolation_level <= TRX_ISO_READ_COMMITTED) {
			/* At READ COMMITTED or READ UNCOMMITTED
			isolation levels, do not lock committed
			delete-marked records. */
			if (!rec_get_deleted_flag(rec, comp)) {
				goto no_gap_lock;
			}

			/* At most one transaction can be active
			for temporary table. */
			if (clust_index->table->is_temporary()) {
				goto no_gap_lock;
			}

			if (index == clust_index) {
				trx_id_t trx_id = row_get_rec_trx_id(
					rec, index, offsets);
				/* In delete-marked records, DB_TRX_ID must
				always refer to an existing undo log record. */
				ut_ad(trx_id);
				if (!trx_sys.is_registered(trx, trx_id)) {
					/* The clustered index record
					was delete-marked in a committed
					transaction. Ignore the record. */
					goto locks_ok_del_marked;
				}
			} else if (trx_t* t = row_vers_impl_x_locked(
					   trx, rec, index, offsets)) {
				/* The record belongs to an active
				transaction. We must acquire a lock. */
				t->release_reference();
			} else {
				/* The secondary index record does not
				point to a delete-marked clustered index
				record that belongs to an active transaction.
				Ignore the secondary index record, because
				it is not locked. */
				goto next_rec;
			}

			goto no_gap_lock;
		}

#ifdef WITH_WSREP
		if (UNIV_UNLIKELY(!set_also_gap_locks)) {
			ut_ad(wsrep_thd_skip_locking(trx->mysql_thd));
			goto no_gap_lock;
		}
#else /* WITH_WSREP */
		ut_ad(set_also_gap_locks);
#endif /* WITH_WSREP */

		/* Set next-key lock both for delete- and non-delete-marked
		records for unique search, because non-delete-marked record can
		be marked as deleted while transaction suspends. */
		if (index->is_spatial()) {
			goto no_gap_lock;
		}

		/* If we are doing a 'greater or equal than a primary key
		value' search from a clustered index, and we find a record
		that has that exact primary key value, then there is no need
		to lock the gap before the record, because no insert in the
		gap can be in our search range. That is, no phantom row can
		appear that way.

		An example: if col1 is the primary key, the search is WHERE
		col1 >= 100, and we find a record where col1 = 100, then no
		need to lock the gap before that record. */

		if (index == clust_index
		    && mode == PAGE_CUR_GE
		    && direction == 0
		    && dtuple_get_n_fields_cmp(search_tuple)
		    == dict_index_get_n_unique(index)
		    && !cmp_dtuple_rec(search_tuple, rec, index, offsets)) {
no_gap_lock:
			lock_type = LOCK_REC_NOT_GAP;
		} else {
			lock_type = LOCK_ORDINARY;
		}

		/* Test hook (debug builds only): allows a BF abort to mark this
		transaction a wsrep victim after the interrupt check at the top of
		rec_loop but before it enqueues a waiting lock request below — the
		window in which the orphaned-waiter bug forms. Inert in release
		builds (DEBUG_SYNC_C compiles to nothing without ENABLED_DEBUG_SYNC). */
		DEBUG_SYNC_C("row_search_before_rec_lock");

		err = sel_set_rec_lock(pcur,
				       rec, index, offsets,
				       prebuilt->select_lock_type,
				       lock_type, thr, &mtr);

		switch (err) {
			const rec_t*	old_vers;
		case DB_SUCCESS_LOCKED_REC:
			if (trx->isolation_level <= TRX_ISO_READ_COMMITTED) {
				/* Note that a record of
				prebuilt->index was locked. */
				prebuilt->new_rec_locks = 1;
			}
			err = DB_SUCCESS;
			/* fall through */
		case DB_SUCCESS:
			break;
		case DB_LOCK_WAIT:
			/* Lock wait for R-tree should already
			be handled in sel_set_rtr_rec_lock() */
			ut_ad(!dict_index_is_spatial(index));
			/* Never unlock rows that were part of a conflict. */
			prebuilt->new_rec_locks = 0;

			if (UNIV_LIKELY(prebuilt->row_read_type
					!= ROW_READ_TRY_SEMI_CONSISTENT)
			    || unique_search
			    || index != clust_index
			    /* If read view was opened, sel_set_rec_lock()
			    would return DB_RECORD_CHANGED, and we would not be
			    here. As read view wasn't opened, do locking read
			    instead of semi-consistent one for READ COMMITTED.
			    For READ UNCOMMITTED
			    row_sel_build_committed_vers_for_mysql() must read
			    uncommitted version of the record. For REPEATABLE
			    READ and SERIALIZABLE prebuilt->row_read_type
			    must be not equal to ROW_READ_TRY_SEMI_CONSISTENT,
			    so there will be locking read for those isolation
			    levels. */
			    || (trx->snapshot_isolation && trx->isolation_level
			      == TRX_ISO_READ_COMMITTED )) {
				if (!prebuilt->skip_locked) {
					goto lock_wait_or_error;
				}
			} else {
				/* The following call returns 'offsets'
				associated with 'old_vers' */
				row_sel_build_committed_vers_for_mysql(
					clust_index, prebuilt, rec,
					&offsets, &heap, &old_vers,
					need_vrow ? &vrow : NULL, &mtr);
			}

			/* Check whether it was a deadlock or not, if not
			a deadlock and the transaction had to wait then
			release the lock it is waiting on. */

			err = lock_trx_handle_wait(trx);

			switch (err) {
			case DB_SUCCESS:
				ut_ad(
				    !trx->lock.was_chosen_as_deadlock_victim);
				/* The lock was granted while we were
				searching for the last committed version.
				Do a normal locking read. */

				offsets = rec_get_offsets(
					rec, index, offsets,
					index->n_core_fields,
					ULINT_UNDEFINED, &heap);
				goto locks_ok;
			case DB_DEADLOCK:
				goto lock_wait_or_error;
			case DB_LOCK_WAIT:
				ut_ad(!dict_index_is_spatial(index));
				err = DB_SUCCESS;
				if (prebuilt->skip_locked) {
					goto next_rec;
				}
				break;
		        case DB_LOCK_WAIT_TIMEOUT:
				if (prebuilt->skip_locked) {
					err = DB_SUCCESS;
					goto next_rec;
				}
				/* fall through */
			default:
				ut_error;
			}

			if (old_vers == NULL) {
				/* The row was not yet committed */

				goto next_rec;
			}

			did_semi_consistent_read = true;
			rec = old_vers;
			break;
		case DB_RECORD_NOT_FOUND:
			if (dict_index_is_spatial(index)) {
				goto next_rec;
			} else {
				goto lock_wait_or_error;
			}
			break;
		case DB_LOCK_WAIT_TIMEOUT:
			if (prebuilt->skip_locked) {
				err = DB_SUCCESS;
				goto next_rec;
			}
			/* fall through */
		default:

			goto lock_wait_or_error;
		}
	} else {
		/* This is a non-locking consistent read: if necessary, fetch
		a previous version of the record */

		if (trx->isolation_level == TRX_ISO_READ_UNCOMMITTED
		    || prebuilt->table->is_temporary()
		    || prebuilt->table->no_rollback()) {

			/* Do nothing: we let a non-locking SELECT read the
			latest version of the record */

		} else if (index == clust_index) {

			/* Fetch a previous version of the row if the current
			one is not visible in the snapshot; if we have a very
			high force recovery level set, we try to avoid crashes
			by skipping this lookup */

			err = row_sel_clust_sees(rec, *index, offsets,
						 trx->read_view);

			switch (err) {
			default:
				goto lock_wait_or_error;
			case DB_SUCCESS:
				break;
			case DB_SUCCESS_LOCKED_REC:
				ut_ad(srv_force_recovery
				      < SRV_FORCE_NO_UNDO_LOG_SCAN);
				rec_t*	old_vers;
				/* The following call returns 'offsets'
				associated with 'old_vers' */
				err = row_sel_build_prev_vers_for_mysql(
					prebuilt, clust_index,
					rec, &offsets, &heap, &old_vers,
					need_vrow ? &vrow : nullptr, &mtr);

				if (err != DB_SUCCESS) {

					goto lock_wait_or_error;
				}

				if (old_vers == NULL) {
					/* The row did not exist yet in
					the read view */

					goto next_rec;
				}

				rec = old_vers;
			}
		} else {
			/* We are looking into a non-clustered index,
			and to get the right version of the record we
			have to look also into the clustered index: this
			is necessary, because we can only get the undo
			information via the clustered index record. */

			ut_ad(!dict_index_is_clust(index));

			if (!srv_read_only_mode) {
				trx_id_t trx_id = page_get_max_trx_id(
					btr_pcur_get_page(pcur));
				ut_ad(trx_id);
				if (trx->read_view.sees(trx_id)) {
					goto locks_ok;
				}
				/* We should look at the clustered index.
				However, as this is a non-locking read,
				we can skip the clustered index lookup if
				the condition does not match the secondary
				index entry. */
				switch (row_search_idx_cond_check(
						buf, prebuilt, rec, offsets)) {
				case CHECK_NEG:
					goto next_rec;
                                case CHECK_ABORTED_BY_USER:
					err = DB_INTERRUPTED;
					goto idx_cond_failed;
				case CHECK_OUT_OF_RANGE:
				case CHECK_ERROR:
					err = DB_RECORD_NOT_FOUND;
					goto idx_cond_failed;
				case CHECK_POS:
					goto requires_clust_rec;
				}

				ut_error;
			}
		}
	}

locks_ok:
	/* NOTE that at this point rec can be an old version of a clustered
	index record built for a consistent read. We cannot assume after this
	point that rec is on a buffer pool page. Functions like
	page_rec_is_comp() cannot be used! */

	if (rec_get_deleted_flag(rec, comp)) {
locks_ok_del_marked:
		/* In delete-marked records, DB_TRX_ID must
		always refer to an existing undo log record. */
		ut_ad(index != clust_index
		      || row_get_rec_trx_id(rec, index, offsets));

		/* The record is delete-marked: we can skip it */

		/* This is an optimization to skip setting the next key lock
		on the record that follows this delete-marked record. This
		optimization works because of the unique search criteria
		which precludes the presence of a range lock between this
		delete marked record and the record following it.

		For now this is applicable only to clustered indexes while
		doing a unique search except for HANDLER queries because
		HANDLER allows NEXT and PREV even in unique search on
		clustered index. There is scope for further optimization
		applicable to unique secondary indexes. Current behaviour is
		to widen the scope of a lock on an already delete marked record
		if the same record is deleted twice by the same transaction */
		if (index == clust_index && unique_search
		    && !prebuilt->used_in_HANDLER) {

			err = DB_RECORD_NOT_FOUND;

			goto normal_return;
		}

		goto next_rec;
	}

	/* Check if the record matches the index condition. */
	switch (row_search_idx_cond_check(buf, prebuilt, rec, offsets)) {
	case CHECK_NEG:
		if (did_semi_consistent_read) {
			row_unlock_for_mysql(prebuilt, TRUE);
		}
		goto next_rec;
        case CHECK_ABORTED_BY_USER:
		err = DB_INTERRUPTED;
		goto idx_cond_failed;
	case CHECK_OUT_OF_RANGE:
        case CHECK_ERROR:
		err = DB_RECORD_NOT_FOUND;
		goto idx_cond_failed;
	case CHECK_POS:
		break;
	}

	if (index != clust_index && prebuilt->need_to_access_clustered) {
		if (row_search_with_covering_prefix(prebuilt, rec, offsets)) {
			goto use_covering_index;
		}
requires_clust_rec:
		ut_ad(index != clust_index);
		/* We use a 'goto' to the preceding label if a consistent
		read of a secondary index record requires us to look up old
		versions of the associated clustered index record. */

		ut_ad(rec_offs_validate(rec, index, offsets));

		/* It was a non-clustered index and we must fetch also the
		clustered index record */

		mtr_extra_clust_savepoint = mtr.get_savepoint();

		ut_ad(!vrow);
		/* The following call returns 'offsets' associated with
		'clust_rec'. Note that 'clust_rec' can be an old version
		built for a consistent read. */

		err = row_sel_get_clust_rec_for_mysql(prebuilt, index, rec,
						      thr, &clust_rec,
						      &offsets, &heap,
						      need_vrow ? &vrow : NULL,
						      &mtr);
		if (err == DB_LOCK_WAIT && prebuilt->skip_locked) {
			err = lock_trx_handle_wait(trx);
		}
		switch (err) {
		case DB_SUCCESS:
			if (clust_rec == NULL) {
				/* The record did not exist in the read view */
				ut_ad(prebuilt->select_lock_type == LOCK_NONE
				      || dict_index_is_spatial(index));
				goto next_rec;
			}
			break;
		case DB_SUCCESS_LOCKED_REC:
			ut_a(clust_rec != NULL);
			if (trx->isolation_level <= TRX_ISO_READ_COMMITTED) {
				/* Note that the clustered index record
				was locked. */
				prebuilt->new_rec_locks = 2;
			}
			err = DB_SUCCESS;
			break;
		case DB_LOCK_WAIT_TIMEOUT:
		case DB_LOCK_WAIT:
			if (prebuilt->skip_locked) {
				err = DB_SUCCESS;
				goto next_rec;
			}
			/* fall through */
		default:
			vrow = NULL;
			goto lock_wait_or_error;
		}

		if (rec_get_deleted_flag(clust_rec, comp)) {

			/* The record is delete marked: we can skip it */

			if (trx->isolation_level <= TRX_ISO_READ_COMMITTED
			    && prebuilt->select_lock_type != LOCK_NONE) {

				/* No need to keep a lock on a delete-marked
				record if we do not want to use next-key
				locking. */

				row_unlock_for_mysql(prebuilt, TRUE);
			}

			goto next_rec;
		}

		if (need_vrow && !vrow) {
			if (!heap) {
				heap = mem_heap_create(100);
			}
			row_sel_fill_vrow(rec, index, &vrow, heap);
		}

		result_rec = clust_rec;
		ut_ad(rec_offs_validate(result_rec, clust_index, offsets));

		if (prebuilt->pk_filter || prebuilt->idx_cond) {
			/* Convert the record to MySQL format. We were
			unable to do this in row_search_idx_cond_check(),
			because the condition is on the secondary index
			and the requested column is in the clustered index.
			We convert all fields, including those that
			may have been used in ICP, because the
			secondary index may contain a column prefix
			rather than the full column. Also, as noted
			in Bug #56680, the column in the secondary
			index may be in the wrong case, and the
			authoritative case is in result_rec, the
			appropriate version of the clustered index record. */
			if (!row_sel_store_mysql_rec(
				    buf, prebuilt, result_rec, vrow,
				    true, clust_index, offsets)) {
				goto next_rec;
			}
		}
	} else {
use_covering_index:
		result_rec = rec;
	}

	/* We found a qualifying record 'result_rec'. At this point,
	'offsets' are associated with 'result_rec'. */

	ut_ad(rec_offs_validate(result_rec,
				result_rec != rec ? clust_index : index,
				offsets));
	ut_ad(!rec_get_deleted_flag(result_rec, comp));

	/* Decide whether to prefetch extra rows.
	At this point, the clustered index record is protected
	by a page latch that was acquired when pcur was positioned.
	The latch will not be released until mtr.commit(). */

	if ((match_mode == ROW_SEL_EXACT
	     || prebuilt->n_rows_fetched >= MYSQL_FETCH_CACHE_THRESHOLD)
	    && prebuilt->select_lock_type == LOCK_NONE
	    && !prebuilt->templ_contains_blob
	    && !prebuilt->clust_index_was_generated
	    && !prebuilt->used_in_HANDLER
	    && !prebuilt->in_fts_query) {
		/* Inside an update, for example, we do not cache rows,
		since we may use the cursor position to do the actual
		update, that is why we require ...lock_type == LOCK_NONE.
		Since we keep space in prebuilt only for the BLOBs of
		a single row, we cannot cache rows in the case there
		are BLOBs in the fields to be fetched. In HANDLER we do
		not cache rows because there the cursor is a scrollable
		cursor. */

		ut_a(prebuilt->n_fetch_cached < MYSQL_FETCH_CACHE_SIZE);

		/* We only convert from InnoDB row format to MySQL row
		format when ICP is disabled. */

		if (!prebuilt->pk_filter && !prebuilt->idx_cond) {
			/* We use next_buf to track the allocation of buffers
			where we store and enqueue the buffers for our
			pre-fetch optimisation.

			If next_buf == 0 then we store the converted record
			directly into the MySQL record buffer (buf). If it is
			!= 0 then we allocate a pre-fetch buffer and store the
			converted record there.

			If the conversion fails and the MySQL record buffer
			was not written to then we reset next_buf so that
			we can re-use the MySQL record buffer in the next
			iteration. */

			next_buf = next_buf
				 ? row_sel_fetch_last_buf(prebuilt) : buf;

			if (!row_sel_store_mysql_rec(
				next_buf, prebuilt, result_rec, vrow,
				result_rec != rec,
				result_rec != rec ? clust_index : index,
				offsets)) {

				if (next_buf == buf) {
					ut_a(prebuilt->n_fetch_cached == 0);
					next_buf = 0;
				}

				/* Only fresh inserts may contain incomplete
				externally stored columns. Pretend that such
				records do not exist. Such records may only be
				accessed at the READ UNCOMMITTED isolation
				level or when rolling back a recovered
				transaction. Rollback happens at a lower
				level, not here. */
				goto next_rec;
			}

			if (next_buf != buf) {
				row_sel_enqueue_cache_row_for_mysql(
					next_buf, prebuilt);
			}
		} else {
			row_sel_enqueue_cache_row_for_mysql(buf, prebuilt);
		}

		if (prebuilt->n_fetch_cached < MYSQL_FETCH_CACHE_SIZE) {
			goto next_rec;
		}
	} else {
		if (!prebuilt->pk_filter && !prebuilt->idx_cond) {
			/* The record was not yet converted to MySQL format. */
			if (!row_sel_store_mysql_rec(
				    buf, prebuilt, result_rec, vrow,
				    result_rec != rec,
				    result_rec != rec ? clust_index : index,
				    offsets)) {
				/* Only fresh inserts may contain
				incomplete externally stored
				columns. Pretend that such records do
				not exist. Such records may only be
				accessed at the READ UNCOMMITTED
				isolation level or when rolling back a
				recovered transaction. Rollback
				happens at a lower level, not here. */
				goto next_rec;
			}
		}

		if (!prebuilt->clust_index_was_generated) {
		} else if (result_rec != rec || index->is_primary()) {
			memcpy(prebuilt->row_id, result_rec, DATA_ROW_ID_LEN);
		} else {
			ulint len;
			const byte* data = rec_get_nth_field(
				result_rec, offsets, index->n_fields - 1,
				&len);
			ut_ad(dict_index_get_nth_col(index,
						     index->n_fields - 1)
			      ->prtype == (DATA_ROW_ID | DATA_NOT_NULL));
			ut_ad(len == DATA_ROW_ID_LEN);
			memcpy(prebuilt->row_id, data, DATA_ROW_ID_LEN);
		}
	}

	/* From this point on, 'offsets' are invalid. */

	/* We have an optimization to save CPU time: if this is a consistent
	read on a unique condition on the clustered index, then we do not
	store the pcur position, because any fetch next or prev will anyway
	return 'end of file'. Exceptions are locking reads and the MySQL
	HANDLER command where the user can move the cursor with PREV or NEXT
	even after a unique search. */

	err = DB_SUCCESS;

idx_cond_failed:
	if (!unique_search
	    || !dict_index_is_clust(index)
	    || direction != 0
	    || prebuilt->select_lock_type != LOCK_NONE
	    || prebuilt->used_in_HANDLER) {

		/* Inside an update always store the cursor position */

		if (!spatial_search) {
			btr_pcur_store_position(pcur, &mtr);
		}
	}

	goto normal_return;

next_rec:
	/* Reset the old and new "did semi-consistent read" flags. */
	if (UNIV_UNLIKELY(prebuilt->row_read_type
			  == ROW_READ_DID_SEMI_CONSISTENT)) {
		prebuilt->row_read_type = ROW_READ_TRY_SEMI_CONSISTENT;
	}
next_rec_after_check:
	did_semi_consistent_read = false;
	prebuilt->new_rec_locks = 0;
	vrow = NULL;

	/*-------------------------------------------------------------*/
	/* PHASE 5: Move the cursor to the next index record */

	/* NOTE: For moves_up==FALSE, the mini-transaction will be
	committed and restarted every time when switching b-tree
	pages. For moves_up==TRUE in index condition pushdown, we can
	scan an entire secondary index tree within a single
	mini-transaction. As long as the prebuilt->idx_cond does not
	match, we do not need to consult the clustered index or
	return records to MySQL, and thus we can avoid repositioning
	the cursor. What prevents us from buffer-fixing all leaf pages
	within the mini-transaction is the btr_leaf_page_release()
	call in btr_pcur_move_to_next_page(). Only the leaf page where
	the cursor is positioned will remain buffer-fixed.
	For R-tree spatial search, we also commit the mini-transaction
	each time  */

	if (spatial_search) {
		/* No need to do store restore for R-tree */
		mtr.rollback_to_savepoint(0);
	} else if (mtr_extra_clust_savepoint) {
		/* We must release any clustered index latches
		if we are moving to the next non-clustered
		index record, because we could break the latching
		order if we would access a different clustered
		index page right away without releasing the previous. */
		mtr.rollback_to_savepoint(mtr_extra_clust_savepoint);
	}

	mtr_extra_clust_savepoint = 0;

	if (moves_up) {
		if (UNIV_UNLIKELY(spatial_search)) {
			if (rtr_pcur_move_to_next(
				    search_tuple, mode, pcur, 0, &mtr)) {
				goto rec_loop;
			}
		} else {
			/* This is based on btr_pcur_move_to_next() */
			ut_ad(pcur->pos_state == BTR_PCUR_IS_POSITIONED);
			ut_ad(pcur->latch_mode != BTR_NO_LATCHES);
			pcur->old_rec = nullptr;
			if (btr_pcur_is_after_last_on_page(pcur)) {
				if (btr_pcur_is_after_last_in_tree(pcur)) {
					goto not_moved;
				}
				err = btr_pcur_move_to_next_page(pcur, &mtr);
				if (err != DB_SUCCESS) {
					goto lock_wait_or_error;
				}
			} else if (!btr_pcur_move_to_next_on_page(pcur)) {
				goto corrupted;
			}

			goto rec_loop;
		}
	} else {
		if (btr_pcur_move_to_prev(pcur, &mtr)) {
			goto rec_loop;
		}
		if (UNIV_UNLIKELY(!btr_pcur_get_rec(pcur))) {
corrupted:
			err = DB_CORRUPTION;
			goto normal_return;
		}
	}

not_moved:
	if (!spatial_search) {
		btr_pcur_store_position(pcur, &mtr);
	}

	err = match_mode ? DB_RECORD_NOT_FOUND : DB_END_OF_INDEX;
	goto normal_return;

lock_wait_or_error:
	if (!dict_index_is_spatial(index)) {
		btr_pcur_store_position(pcur, &mtr);
	}
page_read_error:
	/* Reset the old and new "did semi-consistent read" flags. */
	if (UNIV_UNLIKELY(prebuilt->row_read_type
			  == ROW_READ_DID_SEMI_CONSISTENT)) {
		prebuilt->row_read_type = ROW_READ_TRY_SEMI_CONSISTENT;
	}
	did_semi_consistent_read = false;

lock_table_wait:
	mtr.commit();
	mtr_extra_clust_savepoint = 0;

	trx->error_state = err;
	thr->lock_state = QUE_THR_LOCK_ROW;

	if (row_mysql_handle_errors(&err, trx, thr, nullptr)) {
		/* It was a lock wait, and it ended */

		thr->lock_state = QUE_THR_LOCK_NOLOCK;
		mtr.start();

		/* Table lock waited, go try to obtain table lock
		again */
		if (table_lock_waited) {
			table_lock_waited = FALSE;

			goto wait_table_again;
		}

		if (!dict_index_is_spatial(index)) {
			sel_restore_position_for_mysql(
				&same_user_rec, BTR_SEARCH_LEAF, pcur,
				moves_up, &mtr);
		}

		if (trx->isolation_level <= TRX_ISO_READ_COMMITTED
		    && !same_user_rec) {

			/* Since we were not able to restore the cursor
			on the same user record, we cannot use
			row_unlock_for_mysql() to unlock any records, and
			we must thus reset the new rec lock info. Since
			in lock0lock.cc we have blocked the inheriting of gap
			X-locks, we actually do not have any new record locks
			set in this case.

			Note that if we were able to restore on the 'same'
			user record, it is still possible that we were actually
			waiting on a delete-marked record, and meanwhile
			it was removed by purge and inserted again by some
			other user. But that is no problem, because in
			rec_loop we will again try to set a lock, and
			new_rec_lock_info in trx will be right at the end. */

			prebuilt->new_rec_locks = 0;
		}

		mode = pcur->search_mode;

		goto rec_loop;
	}

	thr->lock_state = QUE_THR_LOCK_NOLOCK;

	goto func_exit;

normal_return:
	mtr.commit();

	DEBUG_SYNC_C("row_search_for_mysql_before_return");

	if (prebuilt->pk_filter || prebuilt->idx_cond) {
		/* When ICP is active we don't write to the MySQL buffer
		directly, only to buffers that are enqueued in the pre-fetch
		queue. We need to dequeue the first buffer and copy the contents
		to the record buffer that was passed in by MySQL. */

		if (prebuilt->n_fetch_cached > 0) {
			row_sel_dequeue_cached_row_for_mysql(buf, prebuilt);
			err = DB_SUCCESS;
		}

	} else if (next_buf != 0) {

		/* We may or may not have enqueued some buffers to the
		pre-fetch queue, but we definitely wrote to the record
		buffer passed to use by MySQL. */

		DEBUG_SYNC_C("row_search_cached_row");
		err = DB_SUCCESS;
	}

#ifdef UNIV_DEBUG
	if (dict_index_is_spatial(index) && err != DB_SUCCESS
	    && err != DB_END_OF_INDEX && err != DB_INTERRUPTED) {
		rtr_node_path_t*	path = pcur->btr_cur.rtr_info->path;

		ut_ad(path->empty());
	}
#endif

func_exit:
	trx->op_info = "";
	if (UNIV_LIKELY_NULL(heap)) {
		mem_heap_free(heap);
	}

	/* Set or reset the "did semi-consistent read" flag on return.
	The flag did_semi_consistent_read is set if and only if
	the record being returned was fetched with a semi-consistent read. */
	ut_ad(prebuilt->row_read_type != ROW_READ_WITH_LOCKS
	      || !did_semi_consistent_read);

	if (prebuilt->row_read_type != ROW_READ_WITH_LOCKS) {
		if (did_semi_consistent_read) {
			prebuilt->row_read_type = ROW_READ_DID_SEMI_CONSISTENT;
		} else {
			prebuilt->row_read_type = ROW_READ_TRY_SEMI_CONSISTENT;
		}
	}

	DEBUG_SYNC_C("innodb_row_search_for_mysql_exit");

	DBUG_RETURN(err);
}

/********************************************************************//**
Count rows in a R-Tree leaf level.
@return DB_SUCCESS if successful */
dberr_t
row_count_rtree_recs(
/*=================*/
	row_prebuilt_t*	prebuilt,	/*!< in: prebuilt struct for the
					table handle; this contains the info
					of search_tuple, index; if search
					tuple contains 0 fields then we
					position the cursor at the start or
					the end of the index, depending on
					'mode' */
	ulint*		n_rows)		/*!< out: number of entries
					seen in the consistent read */
{
	dict_index_t*	index		= prebuilt->index;
	dberr_t		ret		= DB_SUCCESS;
	mtr_t		mtr{prebuilt->trx};
	mem_heap_t*	heap;
	dtuple_t*	entry;
	dtuple_t*	search_entry	= prebuilt->search_tuple;
	ulint		i;
	byte*		buf;

	ut_a(dict_index_is_spatial(index));

	*n_rows = 0;

	heap = mem_heap_create(256);

	/* Build a search tuple. */
	entry = dtuple_create(heap, index->n_fields);

	for (i = 0; i < index->n_fields; i++) {
		const dict_field_t*	ind_field
			= dict_index_get_nth_field(index, i);
		const dict_col_t*	col
			= ind_field->col;
		dfield_t*		dfield
			= dtuple_get_nth_field(entry, i);

		if (i == 0) {
			double*	mbr;
			double	tmp_mbr[SPDIMS * 2];

			dfield->type.mtype = DATA_GEOMETRY;
			dfield->type.prtype |= DATA_GIS_MBR;

			/* Allocate memory for mbr field */
			mbr = static_cast<double*>
				(mem_heap_alloc(heap, DATA_MBR_LEN));

			/* Set mbr field data. */
			dfield_set_data(dfield, mbr, DATA_MBR_LEN);

			for (uint j = 0; j < SPDIMS; j++) {
				tmp_mbr[j * 2] = DBL_MAX;
				tmp_mbr[j * 2 + 1] = -DBL_MAX;
			}
			dfield_write_mbr(dfield, tmp_mbr);
			continue;
		}

		dfield->type.mtype = col->mtype;
		dfield->type.prtype = col->prtype;

	}

	prebuilt->search_tuple = entry;

	ulint bufsize = std::max<ulint>(srv_page_size,
					prebuilt->mysql_row_len);
	buf = static_cast<byte*>(ut_malloc_nokey(bufsize));

	ulint direction = 0;

loop:
	ret = row_search_mvcc(buf, PAGE_CUR_WITHIN, prebuilt, 0, direction);
	direction = ROW_SEL_NEXT;

	switch (ret) {
	case DB_SUCCESS:
		break;
	case DB_DEADLOCK:
	case DB_LOCK_TABLE_FULL:
	case DB_LOCK_WAIT_TIMEOUT:
	case DB_INTERRUPTED:
		goto func_exit;
	default:
		/* fall through (this error is ignored by CHECK TABLE) */
	case DB_END_OF_INDEX:
		ret = DB_SUCCESS;
func_exit:
		prebuilt->search_tuple = search_entry;
		ut_free(buf);
		mem_heap_free(heap);

		return(ret);
	}

	++*n_rows;
	goto loop;
}

/** Check if a version of a clustered index record and a secondary
index record match.

@param prebuilt       index and transaction
@param clust_rec      a version of a clustered index record
@param clust_index    clustered index
@param clust_offsets  rec_get_offsets(clust_rec, clust_index)
@param rec            secondary index leaf page record
@param offsets        rec_get_offsets(rec, index)
@return an error code
@retval DB_SUCCESS             if rec matches clust_rec
@retval DB_SUCCESS_LOCKED_REC  if rec does not match clust_rec
*/
static dberr_t row_check_index_match(row_prebuilt_t *prebuilt,
                                     const rec_t *clust_rec,
                                     const dict_index_t *clust_index,
                                     const rec_offs *clust_offsets,
                                     const rec_t *rec,
                                     const dict_index_t *index,
                                     const rec_offs *offsets)
{
  ut_ad(index == prebuilt->index);

  ib_vcol_row vc(index->has_virtual() ? mem_heap_create(256) : nullptr);

  const uint16_t n= index->n_user_defined_cols;

  for (uint16_t i= 0; i < n; i++)
  {
    ulint pos= 0;
    ulint len, sec_len;

    const dict_field_t &ifield= index->fields[i];
    const byte *sec_field= rec_get_nth_field(rec, offsets, i, &sec_len);
    const byte *field;

    if (ifield.col->is_virtual())
    {
      /* Virtual column values must be reconstructed from the base columns. */
      row_ext_t *ext;
      byte *record= vc.record(prebuilt->trx->mysql_thd, clust_index,
                              &prebuilt->m_mysql_table);
      const dict_v_col_t *v_col= reinterpret_cast<const dict_v_col_t*>
        (ifield.col);
      dtuple_t *row= row_build(ROW_COPY_POINTERS,
                               clust_index, clust_rec, clust_offsets,
                               nullptr, nullptr, nullptr, &ext, vc.heap);
      if (dfield_t *vfield=
          innobase_get_computed_value(row, v_col, clust_index, &vc.heap,
                                      nullptr, nullptr,
                                      prebuilt->trx->mysql_thd,
                                      prebuilt->m_mysql_table,
                                      record, nullptr, nullptr))
      {
        len= vfield->len;
        field= static_cast<byte*>(vfield->data);
      }
      else
      {
        innobase_report_computed_value_failed(row);
        return DB_COMPUTE_VALUE_FAILED;
      }
    }
    else
    {
      pos= dict_col_get_clust_pos(ifield.col, clust_index);
      field= rec_get_nth_cfield(clust_rec, clust_index, clust_offsets, pos,
                                &len);
      if (len == UNIV_SQL_NULL)
      {
        if (sec_len == UNIV_SQL_NULL)
          continue;
        return DB_SUCCESS_LOCKED_REC;
      }
      if (sec_len == UNIV_SQL_NULL)
        return DB_SUCCESS_LOCKED_REC;

      if (rec_offs_nth_extern(clust_offsets, pos))
      {
        if (len == BTR_EXTERN_FIELD_REF_SIZE)
          goto compare_blobs;
        len-= BTR_EXTERN_FIELD_REF_SIZE;
      }

      if (ifield.prefix_len)
      {
        len=
          dtype_get_at_most_n_mbchars(ifield.col->prtype, ifield.col->mbminlen,
                                      ifield.col->mbmaxlen,
                                      ifield.prefix_len, len,
                                      reinterpret_cast<const char*>(field));
        if (len < sec_len)
          goto check_for_blob;
      }
      else
      {
check_for_blob:
        if (rec_offs_nth_extern(clust_offsets, pos))
        {
compare_blobs:
          if (!row_sel_sec_rec_is_for_blob(ifield.col->mtype,
                                           ifield.col->prtype,
                                           ifield.col->mbminlen,
                                           ifield.col->mbmaxlen,
                                           field, len, sec_field, sec_len,
                                           ifield.prefix_len,
                                           clust_index->table))
            return DB_SUCCESS_LOCKED_REC;
          continue;
        }
      }
    }

    if (cmp_data(ifield.col->mtype, ifield.col->prtype, false,
                 field, len, sec_field, sec_len))
      return DB_SUCCESS_LOCKED_REC;
  }

  return DB_SUCCESS;
}

/**
Check the index records in CHECK TABLE.
The index must contain entries in an ascending order,
unique constraint must not be violated by duplicated keys,
and the number of index entries is counted in according to the
current read view.

@param prebuilt    index and transaction
@param n_rows      number of records counted

@return error code
@retval DB_SUCCESS  if no error was found */
dberr_t row_check_index(row_prebuilt_t *prebuilt, ulint *n_rows)
{
  rec_offs offsets_[REC_OFFS_NORMAL_SIZE];
  rec_offs_init(offsets_);

  *n_rows= 0;
  dict_index_t *const index= prebuilt->index;

  if (!index->is_btree())
    return DB_CORRUPTION;

  mem_heap_t *heap= mem_heap_create(100);

  dtuple_t *prev_entry= nullptr;
  trx_t *const trx{prebuilt->trx};
  mtr_t mtr{trx};
  mtr.start();

  dict_index_t *clust_index= dict_table_get_first_index(prebuilt->table);
  prebuilt->clust_pcur->btr_cur.page_cur.index = clust_index;
  dberr_t err= prebuilt->pcur->open_leaf(true, index, BTR_SEARCH_LEAF, &mtr);
  if (UNIV_UNLIKELY(err != DB_SUCCESS))
  {
func_exit:
    mtr.commit();
    mem_heap_free(heap);
    return err;
  }

  if (const trx_id_t bulk_trx_id= index->table->bulk_trx_id)
    if (!trx->read_view.changes_visible(bulk_trx_id))
      goto func_exit;

  ReadView check_table_extended_view;
  ReadView &view=
    prebuilt->need_to_access_clustered &&
    !prebuilt->table->is_temporary() &&
    trx->isolation_level != TRX_ISO_READ_UNCOMMITTED
    ? check_table_extended_view : trx->read_view;
  if (&view == &check_table_extended_view)
    check_table_extended_view.set_creator_trx_id(trx->id);

page_loop:
  if (&view == &check_table_extended_view)
    /* In CHECK TABLE...EXTENDED, we make a copy of purge_sys.end_view
    while holding a shared latch on the index leaf page.
    Should a currently active purge batch desire to remove any further
    records from this page, it would be blocked by our page latch.

    We will consult check_table_extended_view to determine if a
    clustered index record corresponding to a secondary index record
    is visible to the current purge batch. Right after we have made our
    copy, purge_sys.end_view is free to be changed again.

    If we have an orphan secondary index record, we may attempt to
    request a clustered index record version that cannot be retrieved
    any more because the undo log records may have been freed
    (according to the purge_sys.end_view). In such a case,
    trx_undo_get_undo_rec() would cause
    trx_undo_prev_version_build() and trx_undo_prev_version_build()
    to return DB_MISSING_HISTORY. */
    static_cast<ReadViewBase&>(check_table_extended_view)=
      purge_sys_t::end_view_guard{}.view();

rec_loop:
  ut_ad(err == DB_SUCCESS);

  if (!btr_pcur_move_to_next_on_page(prebuilt->pcur))
  {
    err= DB_CORRUPTION;
    goto func_exit;
  }

  const rec_t *rec= btr_pcur_get_rec(prebuilt->pcur);
  rec_offs *offsets= offsets_;

  if (page_rec_is_supremum(rec))
  {
  next_page:
    if (btr_pcur_is_after_last_in_tree(prebuilt->pcur))
      goto func_exit;
    err= btr_pcur_move_to_next_page(prebuilt->pcur, &mtr);
    if (err == DB_SUCCESS && trx_is_interrupted(trx))
      err= DB_INTERRUPTED;
    if (UNIV_UNLIKELY(err != DB_SUCCESS))
      goto func_exit;
    goto page_loop;
  }

  offsets= rec_get_offsets(rec, index, offsets, index->n_core_fields,
                           ULINT_UNDEFINED, &heap);

  const auto info_bits=
    rec_get_info_bits(rec, prebuilt->table->not_redundant());
  const bool rec_deleted= info_bits & REC_INFO_DELETED_FLAG;

  if (UNIV_UNLIKELY(info_bits & REC_INFO_MIN_REC_FLAG))
  {
    if (*n_rows || !index->is_instant())
    {
      push_warning_printf(trx->mysql_thd,
                          Sql_condition::WARN_LEVEL_WARN, ER_NOT_KEYFILE,
                          "InnoDB: invalid record encountered");
      prebuilt->autoinc_error= DB_INDEX_CORRUPT;
    }
    goto next_rec;
  }

  if (prebuilt->table->is_temporary())
  {
  count_or_not:
    if (rec_deleted)
      goto next_rec;
  }
  else if (index->is_clust())
  {
    if (trx->isolation_level == TRX_ISO_READ_UNCOMMITTED)
      goto count_or_not;

    trx_id_t rec_trx_id= row_get_rec_trx_id(rec, index, offsets);

    if (rec_trx_id >= trx->read_view.low_limit_id() &&
        UNIV_UNLIKELY(rec_trx_id >= trx_sys.get_max_trx_id()))
    {
    invalid_trx_id:
      if (prebuilt->autoinc_error == DB_SUCCESS)
        push_warning_printf(trx->mysql_thd, Sql_condition::WARN_LEVEL_WARN,
                            ER_NOT_KEYFILE,
                            "InnoDB: DB_TRX_ID=" TRX_ID_FMT
                            " exceeds the system-wide maximum",
                            rec_trx_id);
      prebuilt->autoinc_error= DB_CORRUPTION;
      goto next_rec;
    }

    if (!trx->read_view.changes_visible(rec_trx_id))
    {
      ut_ad(srv_force_recovery < SRV_FORCE_NO_UNDO_LOG_SCAN);
      rec_t *old_vers;
      /* The following call returns 'offsets' associated with 'old_vers' */
      err= row_sel_build_prev_vers_for_mysql(prebuilt, index, rec, &offsets,
                                             &heap, &old_vers, nullptr, &mtr);

      if (err != DB_SUCCESS)
        goto func_exit;

      if (old_vers)
      {
        rec= old_vers;
        rec_trx_id= row_get_rec_trx_id(rec, index, offsets);

        if (rec_trx_id >= trx->read_view.low_limit_id() &&
            UNIV_UNLIKELY(rec_trx_id >= trx_sys.get_max_trx_id()))
          goto invalid_trx_id;

        if (!rec_get_deleted_flag(rec, prebuilt->table->not_redundant()))
          goto count_row;
      }
      else
        offsets= rec_get_offsets(rec, index, offsets, index->n_core_fields,
                                 ULINT_UNDEFINED, &heap);
      goto next_rec;
    }
    else if (!rec_deleted);
    else if (!check_table_extended_view.changes_visible(rec_trx_id));
    else if (prebuilt->autoinc_error == DB_SUCCESS)
    {
      ib::warn w;
      w << "Unpurged clustered index record in table "
        << index->table->name << ": "
        << rec_offsets_print(rec, offsets);
      prebuilt->autoinc_error= DB_MISSING_HISTORY;
      push_warning_printf(trx->mysql_thd, Sql_condition::WARN_LEVEL_WARN,
                          ER_NOT_KEYFILE, "InnoDB: %s", w.m_oss.str().c_str());
    }

    goto count_or_not;
  }
  else if (const trx_id_t page_trx_id=
           page_get_max_trx_id(btr_pcur_get_page(prebuilt->pcur)))
  {
    if (page_trx_id >= trx_sys.get_max_trx_id())
      goto invalid_PAGE_MAX_TRX_ID;
    if (trx->isolation_level == TRX_ISO_READ_UNCOMMITTED);
    else if (&view == &check_table_extended_view || rec_deleted ||
             !view.sees(page_trx_id))
    {
      bool got_extended_match= &view == &check_table_extended_view;
      const auto savepoint= mtr.get_savepoint();

      row_build_row_ref_in_tuple(prebuilt->clust_ref, rec, index, offsets);
      err= btr_pcur_open_with_no_init(prebuilt->clust_ref,
                                      PAGE_CUR_LE, BTR_SEARCH_LEAF,
                                      prebuilt->clust_pcur, &mtr);
      if (err != DB_SUCCESS)
        goto func_exit;

      const rec_t *clust_rec= btr_pcur_get_rec(prebuilt->clust_pcur);

      /* Note: only if the search ends up on a non-infimum record is the
      low_match value the real match to the search tuple */

      if (!page_rec_is_user_rec(clust_rec) ||
          btr_pcur_get_low_match(prebuilt->clust_pcur) < clust_index->n_uniq)
      {
        if (!rec_deleted)
        {
        not_found:
          /* MDEV-29823 FIXME: There is a race condition between
          rollback, purge, and possibly other SQL connections that
          are creating and releasing read views. At the time
          row_undo_mod_del_mark_or_remove_sec_low() is executing
          rollback on a secondary index record, purge_sys.view
          may not allow it to delete the record, and it will be
          delete-marked. Eventually purge_sys.view would advance,
          but the delete-marked record could never be removed,
          because no undo log record was ever added to
          the purge queue by trx_purge_add_undo_to_history().

          For now, we will not flag an error about orphan secondary index
          records that are delete-marked; we will only warn about them. */

          if (!rec_deleted || prebuilt->autoinc_error == DB_SUCCESS)
          {
            ib::error_or_warn w(!rec_deleted);
            w << "Clustered index record not found for index "
              << index->name << " of table " << index->table->name
              << ": " << rec_offsets_print(rec, offsets);
            push_warning_printf(trx->mysql_thd, Sql_condition::WARN_LEVEL_WARN,
                                ER_NOT_KEYFILE, "InnoDB: %s",
                                w.m_oss.str().c_str());
          }

          if (prebuilt->autoinc_error == DB_SUCCESS)
            prebuilt->autoinc_error= rec_deleted
              ? DB_MISSING_HISTORY
              : DB_CORRUPTION;
        }
        else if (&view == &check_table_extended_view)
        extended_not_found:
          if (view.changes_visible(page_trx_id))
            goto not_found;
      did_not_find:
        mtr.rollback_to_savepoint(savepoint);
        goto next_rec;
      }

      rec_offs *clust_offsets;
      trx_id_t rec_trx_id;
      rec_t *old_vers= nullptr;

      bool found_in_view= false;
      trx_id_t visible_trx_id= ~0ULL;

      if (ulint trx_id_offset= clust_index->trx_id_offset)
      {
        clust_offsets= nullptr;
      read_trx_id:
        rec_trx_id= trx_read_trx_id(clust_rec + trx_id_offset);

        if (clust_rec[trx_id_offset + DATA_TRX_ID_LEN] & 0x80)
        {
          if (UNIV_UNLIKELY
              (rec_get_deleted_flag(clust_rec,
                                    prebuilt->table->not_redundant())))
          {
            err= DB_CORRUPTION;
            goto func_exit;
          }

          /* This is the oldest available record version (fresh insert). */
          if (!view.changes_visible(rec_trx_id))
          {
            if (rec_trx_id >= view.low_limit_id() &&
                UNIV_UNLIKELY(rec_trx_id >= trx_sys.get_max_trx_id()))
              goto invalid_rec_trx_id;
            if (got_extended_match)
              goto check_latest_version;
            goto did_not_find;
          }
        }
      }
      else
      {
        clust_offsets= rec_get_offsets(clust_rec, clust_index, nullptr,
                                       clust_index->n_core_fields,
                                       ULINT_UNDEFINED, &heap);
        ulint trx_id_pos= clust_index->n_uniq ? clust_index->n_uniq : 1;
        ulint len;
        trx_id_offset= rec_get_nth_field_offs(clust_offsets, trx_id_pos, &len);
        ut_ad(len == DATA_TRX_ID_LEN);
        goto read_trx_id;
      }

      if (got_extended_match)
      {
      check_latest_version:
        /* In CHECK TABLE...EXTENDED, always check if the secondary
        index record matches the latest clustered index record
        version, no matter if it is visible in our own read view.

        If the latest clustered index version is delete-marked and
        purgeable, it is not safe to fetch any BLOBs for column prefix
        indexes because they may already have been freed. */
        if (rec_trx_id &&
            rec_get_deleted_flag(clust_rec,
                                 prebuilt->table->not_redundant()) &&
            purge_sys.is_purgeable(rec_trx_id))
          goto did_not_find;

        if (!clust_offsets)
          clust_offsets= rec_get_offsets(clust_rec, clust_index, nullptr,
                                         clust_index->n_core_fields,
                                         ULINT_UNDEFINED, &heap);
        err= row_check_index_match(prebuilt,
                                   clust_rec, clust_index, clust_offsets,
                                   rec, index, offsets);

        switch (err) {
        default:
          goto func_exit;
        case DB_SUCCESS_LOCKED_REC:
        case DB_SUCCESS:
          break;
        }

        got_extended_match= err == DB_SUCCESS;
        err= DB_SUCCESS;

        if (!trx->read_view.changes_visible(rec_trx_id))
          /* While CHECK TABLE ... EXTENDED checks for a matching
          clustered index record version for each secondary index
          record, it must count only those records that belong to its
          own read view.

          If the latest version of clust_rec matches rec but is not
          in our read view, there may still be an older version of
          clust_rec that not only matches rec but is in our view.
          We must evaluate old versions before deciding whether rec
          should be counted. */
          goto check_old_vers;

        /* Remember that this is the visible clust_rec for rec,
        and whether it matches rec. */
        visible_trx_id= rec_trx_id;
        found_in_view= got_extended_match &&
          !rec_get_deleted_flag(clust_rec,
                                prebuilt->table->not_redundant());

        if (!got_extended_match)
          goto check_old_vers;

        if (!found_in_view)
          goto did_not_find;

      found_match:
        mtr.rollback_to_savepoint(savepoint);
        goto count_row;
      }
      else if (!view.changes_visible(rec_trx_id))
      {
      check_old_vers:
        if (rec_trx_id >= view.low_limit_id() &&
            UNIV_UNLIKELY(rec_trx_id >= trx_sys.get_max_trx_id()))
        {
        invalid_rec_trx_id:
          if (prebuilt->autoinc_error == DB_SUCCESS)
            push_warning_printf(trx->mysql_thd, Sql_condition::WARN_LEVEL_WARN,
                                ER_NOT_KEYFILE,
                                "InnoDB: DB_TRX_ID=" TRX_ID_FMT
                                " exceeds the system-wide maximum",
                                rec_trx_id);
          goto not_found;
        }

        if (!clust_offsets)
          clust_offsets= rec_get_offsets(clust_rec, clust_index, nullptr,
                                         clust_index->n_core_fields,
                                         ULINT_UNDEFINED, &heap);

        row_sel_reset_old_vers_heap(prebuilt);
        /* The following is adapted from row_vers_build_for_consistent_read()
        because when using check_table_extended_view, we must
        consider every available version of the clustered index record. */
        mem_heap_t *vers_heap= nullptr;

        for (;;)
        {
          mem_heap_t *prev_heap= vers_heap;
          vers_heap= mem_heap_create(1024);
          err= trx_undo_prev_version_build(clust_rec,
                                           clust_index, clust_offsets,
                                           vers_heap, &old_vers,
                                           &mtr, 0, nullptr, nullptr);
          if (prev_heap)
            mem_heap_free(prev_heap);
          if (err != DB_SUCCESS)
          {
          old_vers_err:
            mem_heap_free(vers_heap);
            if (err == DB_MISSING_HISTORY)
            {
              err= DB_SUCCESS;
              if (got_extended_match)
                goto did_not_find;
              goto not_found;
            }
            goto func_exit;
          }

          if (UNIV_UNLIKELY(!old_vers))
          {
            mem_heap_free(vers_heap);
            /* We did not find a matching clustered index record version
            for the secondary index record. Normal CHECK TABLE will simply
            not count the secondary index record; CHECK TABLE ... EXTENDED
            will flag such orphan records if appropriate.

            A secondary index record may may be "temporarily orphan"
            if purge is in progress. We will only flag them if
            everything up to PAGE_MAX_TRX_ID has been fully purged.

            "Temporary orphans" may be produced when
            row_undo_mod_clust() resets the DB_TRX_ID of the latest
            clust_rec version or when trx_undo_prev_version_build()
            encounters a BLOB that may have been freed according to
            purge_sys.view (not purge_sys.end_view). */
            if (&view == &check_table_extended_view && !got_extended_match)
              goto extended_not_found;
            goto did_not_find;
          }

          clust_rec= old_vers;
          clust_offsets= rec_get_offsets(clust_rec, clust_index, clust_offsets,
                                         clust_index->n_core_fields,
                                         ULINT_UNDEFINED, &heap);

          rec_trx_id= row_get_rec_trx_id(clust_rec, clust_index,
                                         clust_offsets);

          if (UNIV_UNLIKELY(rec_trx_id >=
                            trx->read_view.low_limit_id() &&
                            rec_trx_id >= trx_sys.get_max_trx_id()))
          {
            mem_heap_free(vers_heap);
            goto invalid_rec_trx_id;
          }

          const bool rec_visible=
            trx->read_view.changes_visible(rec_trx_id);
          const bool clust_rec_deleted=
            rec_get_deleted_flag(clust_rec, prebuilt->table->not_redundant());

          if (&view != &trx->read_view)
          {
            /* It is not safe to fetch BLOBs of committed delete-marked
            records that may have been freed in purge. */
            err= clust_rec_deleted && rec_trx_id &&
              purge_sys.is_purgeable(rec_trx_id)
              ? DB_SUCCESS_LOCKED_REC
              : row_check_index_match(prebuilt,
                                      clust_rec, clust_index, clust_offsets,
                                      rec, index, offsets);

            switch (err) {
            default:
              goto old_vers_err;
            case DB_SUCCESS_LOCKED_REC:
              if (rec_visible && !~visible_trx_id)
                visible_trx_id= rec_trx_id;
              continue;
            case DB_SUCCESS:
              got_extended_match= true;
              if (!rec_visible)
                continue;
              if (!~visible_trx_id)
              {
                visible_trx_id= rec_trx_id;
                found_in_view= !clust_rec_deleted;
              }
              mem_heap_free(vers_heap);
              if (!found_in_view)
                goto did_not_find;
              goto found_match;
            }
          }
          else if (rec_visible)
          {
            if (!clust_rec_deleted)
            {
              clust_rec= rec_copy(mem_heap_alloc(heap,
                                                 rec_offs_size(clust_offsets)),
                                  clust_rec, clust_offsets);
              rec_offs_make_valid(clust_rec, clust_index, true, clust_offsets);
            }
            mem_heap_free(vers_heap);
            if (clust_rec_deleted)
              goto did_not_find;
            goto check_match;
          }
        }
      }
      else if (rec_get_deleted_flag(clust_rec,
                                    prebuilt->table->not_redundant()))
        goto did_not_find;

      ut_ad(clust_rec);
      ut_ad(&view != &check_table_extended_view);

      /* If we had to go to an earlier version of row or the secondary
      index record is delete marked, then it may be that the secondary
      index record corresponding to clust_rec (or old_vers) is not
      rec; in that case we must ignore such row because in our
      snapshot rec would not have existed. Remember that from rec we
      cannot see directly which transaction id corresponds to it: we
      have to go to the clustered index record. A query where we want
      to fetch all rows where the secondary index value is in some
      interval would return a wrong result if we would not drop rows
      which we come to visit through secondary index records that
      would not really exist in our snapshot. */

      if (rec_deleted)
      {
        if (!clust_offsets)
          clust_offsets= rec_get_offsets(clust_rec, clust_index, nullptr,
                                         clust_index->n_core_fields,
                                         ULINT_UNDEFINED, &heap);
      check_match:
        /* This clustered index record version exists in
        trx->read_view and is not delete-marked.
        By design, any BLOBs in it are not allowed to be
        freed in the purge of committed transaction history. */
        err= row_check_index_match(prebuilt, clust_rec, clust_index,
                                   clust_offsets, rec, index, offsets);
        switch (err) {
        case DB_SUCCESS:
          break;
        case DB_SUCCESS_LOCKED_REC:
          err= DB_SUCCESS;
          goto did_not_find;
        default:
          goto func_exit;
        }
      }

      mtr.rollback_to_savepoint(savepoint);
    }
  }
  else
  {
  invalid_PAGE_MAX_TRX_ID:
    if (UNIV_LIKELY(srv_force_recovery < SRV_FORCE_NO_UNDO_LOG_SCAN))
    {
      push_warning_printf(trx->mysql_thd,
                          Sql_condition::WARN_LEVEL_WARN, ER_NOT_KEYFILE,
                          "InnoDB: Invalid PAGE_MAX_TRX_ID=%" PRIu64
                          " in index '%-.200s'",
                          page_trx_id, index->name());
      prebuilt->autoinc_error= DB_INDEX_CORRUPT;
    }
    goto next_rec;
  }

count_row:
  ++*n_rows;

  if (prev_entry)
  {
    uint16_t matched= 0;
    int cmp= cmp_dtuple_rec_with_match(prev_entry, rec, index, offsets,
                                       &matched);
    const char* msg;

    if (UNIV_LIKELY(cmp < 0));
    else if (cmp > 0)
    {
      prebuilt->autoinc_error= DB_INDEX_CORRUPT;
      msg= "index records in a wrong order in ";
not_ok:
      ib::error() << msg << index->name << " of table " << index->table->name
                  << ": " << *prev_entry << ", "
                  << rec_offsets_print(rec, offsets);
    }
    else if (index->is_unique() && matched >=
             dict_index_get_n_ordering_defined_by_user(index))
    {
      /* NULL values in unique indexes are considered not to be duplicates */
      for (ulint i= 0; i < dict_index_get_n_ordering_defined_by_user(index);
           i++)
        if (dfield_is_null(dtuple_get_nth_field(prev_entry, i)))
          goto next_rec;

      if (prebuilt->autoinc_error == DB_SUCCESS)
        prebuilt->autoinc_error= DB_DUPLICATE_KEY;
      msg= "duplicate key in ";
      goto not_ok;
    }
  }

next_rec:
  ut_ad(err == DB_SUCCESS);

  {
    mem_heap_t *tmp_heap= nullptr;

    /* Empty the heap on each round.  But preserve offsets[]
    for the row_rec_to_index_entry() call, by copying them
    into a separate memory heap when needed. */
    if (UNIV_UNLIKELY(offsets != offsets_))
    {
      ulint size= rec_offs_get_n_alloc(offsets) * sizeof *offsets;
      tmp_heap= mem_heap_create(size);
      offsets= static_cast<rec_offs*>(mem_heap_dup(tmp_heap, offsets, size));
    }

    mem_heap_empty(heap);
    prev_entry= row_rec_to_index_entry(rec, index, offsets, heap);

    if (UNIV_LIKELY_NULL(tmp_heap))
      mem_heap_free(tmp_heap);
  }

  if (btr_pcur_is_after_last_on_page(prebuilt->pcur))
    goto next_page;

  goto rec_loop;
}
