class Sequel::ShardedThreadedConnectionPool
The slowest and most advanced connection pool, dealing with both multi-threaded access and configurations with multiple shards/servers.
In addition, this pool subclass also handles scheduling in-use connections to be removed from the pool when they are returned to it.
Public Class Methods
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 18 def initialize(db, opts = OPTS) 19 super 20 @available_connections = {} 21 @connections_to_remove = [] 22 @connections_to_disconnect = [] 23 @servers = opts.fetch(:servers_hash, Hash.new(:default)) 24 remove_instance_variable(:@waiter) 25 remove_instance_variable(:@allocated) 26 @allocated = {} 27 @waiters = {} 28 29 add_servers([:default]) 30 add_servers(opts[:servers].keys) if opts[:servers] 31 end
The following additional options are respected:
- :servers
-
A hash of servers to use. Keys should be symbols. If not present, will use a single :default server.
- :servers_hash
-
The base hash to use for the servers. By default,
Sequel
uses Hash.new(:default). You can use a hash with a default proc that raises an error if you want to catch all cases where a nonexistent server is used.
Sequel::ThreadedConnectionPool::new
Public Instance Methods
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 35 def add_servers(servers) 36 sync do 37 servers.each do |server| 38 unless @servers.has_key?(server) 39 @servers[server] = server 40 @available_connections[server] = [] 41 allocated = {} 42 allocated.compare_by_identity 43 @allocated[server] = allocated 44 @waiters[server] = ConditionVariable.new 45 end 46 end 47 end 48 end
Adds new servers to the connection pool. Allows for dynamic expansion of the potential replicas/shards at runtime. servers
argument should be an array of symbols.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 63 def all_connections 64 t = Sequel.current 65 sync do 66 @allocated.values.each do |threads| 67 threads.each do |thread, conn| 68 yield conn if t == thread 69 end 70 end 71 @available_connections.values.each{|v| v.each{|c| yield c}} 72 end 73 end
Yield all of the available connections, and the ones currently allocated to this thread. This will not yield connections currently allocated to other threads, as it is not safe to operate on them. This holds the mutex while it is yielding all of the connections, which means that until the method’s block returns, the pool is locked.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 54 def allocated(server=:default) 55 @allocated[server] 56 end
A hash of connections currently being used for the given server, key is the Thread, value is the connection. Nonexistent servers will return nil. Treat this as read only, do not modify the resulting object. The calling code should already have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 79 def available_connections(server=:default) 80 @available_connections[server] 81 end
An array of connections opened but not currently used, for the given server. Nonexistent servers will return nil. Treat this as read only, do not modify the resulting object. The calling code should already have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 100 def disconnect(opts=OPTS) 101 (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |s| 102 disconnect_connections(sync{disconnect_server_connections(s)}) 103 end 104 end
Removes all connections currently available on all servers, optionally yielding each connection to the given block. This method has the effect of disconnecting from the database, assuming that no connections are currently being used. If connections are being used, they are scheduled to be disconnected as soon as they are returned to the pool.
Once a connection is requested using hold
, the connection pool creates new connections to the database. Options:
- :server
-
Should be a symbol specifing the server to disconnect from, or an array of symbols to specify multiple servers.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 106 def freeze 107 @servers.freeze 108 super 109 end
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# File lib/sequel/connection_pool/sharded_threaded.rb 124 def hold(server=:default) 125 server = pick_server(server) 126 t = Sequel.current 127 if conn = owned_connection(t, server) 128 return yield(conn) 129 end 130 begin 131 conn = acquire(t, server) 132 yield conn 133 rescue Sequel::DatabaseDisconnectError, *@error_classes => e 134 sync{@connections_to_remove << conn} if conn && disconnect_error?(e) 135 raise 136 ensure 137 sync{release(t, conn, server)} if conn 138 while dconn = sync{@connections_to_disconnect.shift} 139 disconnect_connection(dconn) 140 end 141 end 142 end
Chooses the first available connection to the given server, or if none are available, creates a new connection. Passes the connection to the supplied block:
pool.hold(:server1) {|conn| conn.execute('DROP TABLE posts')}
Pool#hold is re-entrant, meaning it can be called recursively in the same thread without blocking.
If no connection is immediately available and the pool is already using the maximum number of connections, Pool#hold will block until a connection is available or the timeout expires. If the timeout expires before a connection can be acquired, a Sequel::PoolTimeout is raised.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 173 def pool_type 174 :sharded_threaded 175 end
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 147 def remove_servers(servers) 148 conns = [] 149 raise(Sequel::Error, "cannot remove default server") if servers.include?(:default) 150 151 sync do 152 servers.each do |server| 153 if @servers.include?(server) 154 conns.concat(disconnect_server_connections(server)) 155 @waiters.delete(server) 156 @available_connections.delete(server) 157 @allocated.delete(server) 158 @servers.delete(server) 159 end 160 end 161 end 162 163 nil 164 ensure 165 disconnect_connections(conns) 166 end
Remove servers from the connection pool. Similar to disconnecting from all given servers, except that after it is used, future requests for the server will use the :default server instead.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 169 def servers 170 sync{@servers.keys} 171 end
Return an array of symbols for servers in the connection pool.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 86 def size(server=:default) 87 @mutex.synchronize{_size(server)} 88 end
The total number of connections opened for the given server. Nonexistent servers will return the created count of the default server. The calling code should NOT have the mutex before calling this.
Private Instance Methods
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 181 def _size(server) 182 server = @servers[server] 183 @allocated[server].length + @available_connections[server].length 184 end
The total number of connections opened for the given server. The calling code should already have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 192 def acquire(thread, server) 193 if conn = assign_connection(thread, server) 194 return conn 195 end 196 197 timeout = @timeout 198 timer = Sequel.start_timer 199 200 if conn = acquire_available(thread, server, timeout) 201 return conn 202 end 203 204 until conn = assign_connection(thread, server) 205 elapsed = Sequel.elapsed_seconds_since(timer) 206 # :nocov: 207 raise_pool_timeout(elapsed, server) if elapsed > timeout 208 209 # It's difficult to get to this point, it can only happen if there is a race condition 210 # where a connection cannot be acquired even after the thread is signalled by the condition variable 211 if conn = acquire_available(thread, server, timeout - elapsed) 212 return conn 213 end 214 # :nocov: 215 end 216 217 conn 218 end
Assigns a connection to the supplied thread, if one is available. The calling code should NOT already have the mutex when calling this.
This should return a connection if one is available within the timeout, or nil if a connection could not be acquired within the timeout.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 221 def acquire_available(thread, server, timeout) 222 sync do 223 # Check if connection was checked in between when assign_connection failed and now. 224 # This is very unlikely, but necessary to prevent a situation where the waiter 225 # will wait for a connection even though one has already been checked in. 226 # :nocov: 227 if conn = next_available(server) 228 return(allocated(server)[thread] = conn) 229 end 230 # :nocov: 231 232 @waiters[server].wait(@mutex, timeout) 233 234 # Connection still not available, could be because a connection was disconnected, 235 # may have to retry assign_connection to see if a new connection can be made. 236 if conn = next_available(server) 237 return(allocated(server)[thread] = conn) 238 end 239 end 240 end
Acquire a connection if one is already available, or waiting until it becomes available.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 244 def assign_connection(thread, server) 245 alloc = nil 246 247 do_make_new = false 248 sync do 249 alloc = allocated(server) 250 if conn = next_available(server) 251 alloc[thread] = conn 252 return conn 253 end 254 255 if (n = _size(server)) >= (max = @max_size) 256 alloc.to_a.each do |t,c| 257 unless t.alive? 258 remove(t, c, server) 259 end 260 end 261 n = nil 262 end 263 264 if (n || _size(server)) < max 265 do_make_new = alloc[thread] = true 266 end 267 end 268 269 # Connect to the database outside of the connection pool mutex, 270 # as that can take a long time and the connection pool mutex 271 # shouldn't be locked while the connection takes place. 272 if do_make_new 273 begin 274 conn = make_new(server) 275 sync{alloc[thread] = conn} 276 ensure 277 unless conn 278 sync{alloc.delete(thread)} 279 end 280 end 281 end 282 283 conn 284 end
Assign a connection to the thread, or return nil if one cannot be assigned. The caller should NOT have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 289 def checkin_connection(server, conn) 290 available_connections(server) << conn 291 @waiters[server].signal 292 conn 293 end
Return a connection to the pool of available connections for the server, returns the connection. The calling code should already have the mutex before calling this.
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# File lib/sequel/connection_pool/sharded_threaded.rb 315 def disconnect_connections(conns) 316 conns.each{|conn| disconnect_connection(conn)} 317 end
Disconnect all available connections immediately, and schedule currently allocated connections for disconnection as soon as they are returned to the pool. The calling code should NOT have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 299 def disconnect_server_connections(server) 300 remove_conns = allocated(server) 301 dis_conns = available_connections(server) 302 raise Sequel::Error, "invalid server: #{server}" unless remove_conns && dis_conns 303 304 @connections_to_remove.concat(remove_conns.values) 305 306 conns = dis_conns.dup 307 dis_conns.clear 308 @waiters[server].signal 309 conns 310 end
Clear the array of available connections for the server, returning an array of previous available connections that should be disconnected (or nil if none should be). Mark any allocated connections to be removed when they are checked back in. The calling code should already have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 322 def next_available(server) 323 case @connection_handling 324 when :stack 325 available_connections(server).pop 326 else 327 available_connections(server).shift 328 end 329 end
Return the next available connection in the pool for the given server, or nil if there is not currently an available connection for the server. The calling code should already have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 333 def owned_connection(thread, server) 334 sync{@allocated[server][thread]} 335 end
Returns the connection owned by the supplied thread for the given server, if any. The calling code should NOT already have the mutex before calling this.
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# File lib/sequel/connection_pool/sharded_threaded.rb 338 def pick_server(server) 339 sync{@servers[server]} 340 end
If the server given is in the hash, return it, otherwise, return the default server.
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# File lib/sequel/connection_pool/sharded_threaded.rb 344 def preconnect(concurrent = false) 345 conn_servers = sync{@servers.keys}.map!{|s| Array.new(max_size - _size(s), s)}.flatten! 346 347 if concurrent 348 conn_servers.map!{|s| Thread.new{[s, make_new(s)]}}.map!(&:value) 349 else 350 conn_servers.map!{|s| [s, make_new(s)]} 351 end 352 353 sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}} 354 end
Create the maximum number of connections immediately. The calling code should NOT have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 358 def raise_pool_timeout(elapsed, server) 359 name = db.opts[:name] 360 raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}" 361 end
Raise a PoolTimeout error showing the current timeout, the elapsed time, the server the connection attempt was made to, and the database’s name (if any).
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# File lib/sequel/connection_pool/sharded_threaded.rb 367 def release(thread, conn, server) 368 if @connections_to_remove.include?(conn) 369 remove(thread, conn, server) 370 else 371 conn = allocated(server).delete(thread) 372 373 if @connection_handling == :disconnect 374 @connections_to_disconnect << conn 375 else 376 checkin_connection(server, conn) 377 end 378 end 379 380 if waiter = @waiters[server] 381 waiter.signal 382 end 383 end
Releases the connection assigned to the supplied thread and server. If the server or connection given is scheduled for disconnection, remove the connection instead of releasing it back to the pool. The calling code should already have the mutex before calling this.
Source
# File lib/sequel/connection_pool/sharded_threaded.rb 387 def remove(thread, conn, server) 388 @connections_to_remove.delete(conn) 389 allocated(server).delete(thread) if @servers.include?(server) 390 @connections_to_disconnect << conn 391 end
Removes the currently allocated connection from the connection pool. The calling code should already have the mutex before calling this.