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
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
# 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
Public Instance Methods
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.
# 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
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.
# 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
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.
# File lib/sequel/connection_pool/sharded_threaded.rb 54 def allocated(server=:default) 55 @allocated[server] 56 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 79 def available_connections(server=:default) 80 @available_connections[server] 81 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.
# 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
# File lib/sequel/connection_pool/sharded_threaded.rb 106 def freeze 107 @servers.freeze 108 super 109 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.
# 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
# File lib/sequel/connection_pool/sharded_threaded.rb 173 def pool_type 174 :sharded_threaded 175 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.
# 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
Return an array of symbols for servers in the connection pool.
# File lib/sequel/connection_pool/sharded_threaded.rb 169 def servers 170 sync{@servers.keys} 171 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 86 def size(server=:default) 87 @mutex.synchronize{_size(server)} 88 end
Private Instance Methods
The total number of connections opened for the given server. The calling code should already have the mutex before calling this.
# 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
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.
# 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 sync do 201 @waiters[server].wait(@mutex, timeout) 202 if conn = next_available(server) 203 return(allocated(server)[thread] = conn) 204 end 205 end 206 207 until conn = assign_connection(thread, server) 208 elapsed = Sequel.elapsed_seconds_since(timer) 209 # :nocov: 210 raise_pool_timeout(elapsed, server) if elapsed > timeout 211 212 # It's difficult to get to this point, it can only happen if there is a race condition 213 # where a connection cannot be acquired even after the thread is signalled by the condition variable 214 sync do 215 @waiters[server].wait(@mutex, timeout - elapsed) 216 if conn = next_available(server) 217 return(allocated(server)[thread] = conn) 218 end 219 end 220 # :nocov: 221 end 222 223 conn 224 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 228 def assign_connection(thread, server) 229 alloc = nil 230 231 do_make_new = false 232 sync do 233 alloc = allocated(server) 234 if conn = next_available(server) 235 alloc[thread] = conn 236 return conn 237 end 238 239 if (n = _size(server)) >= (max = @max_size) 240 alloc.to_a.each do |t,c| 241 unless t.alive? 242 remove(t, c, server) 243 end 244 end 245 n = nil 246 end 247 248 if (n || _size(server)) < max 249 do_make_new = alloc[thread] = true 250 end 251 end 252 253 # Connect to the database outside of the connection pool mutex, 254 # as that can take a long time and the connection pool mutex 255 # shouldn't be locked while the connection takes place. 256 if do_make_new 257 begin 258 conn = make_new(server) 259 sync{alloc[thread] = conn} 260 ensure 261 unless conn 262 sync{alloc.delete(thread)} 263 end 264 end 265 end 266 267 conn 268 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 273 def checkin_connection(server, conn) 274 available_connections(server) << conn 275 @waiters[server].signal 276 conn 277 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 299 def disconnect_connections(conns) 300 conns.each{|conn| disconnect_connection(conn)} 301 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 283 def disconnect_server_connections(server) 284 remove_conns = allocated(server) 285 dis_conns = available_connections(server) 286 raise Sequel::Error, "invalid server: #{server}" unless remove_conns && dis_conns 287 288 @connections_to_remove.concat(remove_conns.values) 289 290 conns = dis_conns.dup 291 dis_conns.clear 292 @waiters[server].signal 293 conns 294 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 306 def next_available(server) 307 case @connection_handling 308 when :stack 309 available_connections(server).pop 310 else 311 available_connections(server).shift 312 end 313 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 317 def owned_connection(thread, server) 318 sync{@allocated[server][thread]} 319 end
If the server given is in the hash, return it, otherwise, return the default server.
# File lib/sequel/connection_pool/sharded_threaded.rb 322 def pick_server(server) 323 sync{@servers[server]} 324 end
Create the maximum number of connections immediately. The calling code should NOT have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb 328 def preconnect(concurrent = false) 329 conn_servers = sync{@servers.keys}.map!{|s| Array.new(max_size - _size(s), s)}.flatten! 330 331 if concurrent 332 conn_servers.map!{|s| Thread.new{[s, make_new(s)]}}.map!(&:value) 333 else 334 conn_servers.map!{|s| [s, make_new(s)]} 335 end 336 337 sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}} 338 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).
# File lib/sequel/connection_pool/sharded_threaded.rb 342 def raise_pool_timeout(elapsed, server) 343 name = db.opts[:name] 344 raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}" 345 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 351 def release(thread, conn, server) 352 if @connections_to_remove.include?(conn) 353 remove(thread, conn, server) 354 else 355 conn = allocated(server).delete(thread) 356 357 if @connection_handling == :disconnect 358 @connections_to_disconnect << conn 359 else 360 checkin_connection(server, conn) 361 end 362 end 363 364 if waiter = @waiters[server] 365 waiter.signal 366 end 367 end
Removes the currently allocated connection from the connection pool. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb 371 def remove(thread, conn, server) 372 @connections_to_remove.delete(conn) 373 allocated(server).delete(thread) if @servers.include?(server) 374 @connections_to_disconnect << conn 375 end