class Sequel::ShardedThreadedConnectionPool
The slowest and most advanced connection, 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 {|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 172 def pool_type 173 :sharded_threaded 174 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 = nil 149 sync do 150 raise(Sequel::Error, "cannot remove default server") if servers.include?(:default) 151 servers.each do |server| 152 if @servers.include?(server) 153 conns = disconnect_server_connections(server) 154 @waiters.delete(server) 155 @available_connections.delete(server) 156 @allocated.delete(server) 157 @servers.delete(server) 158 end 159 end 160 end 161 162 if conns 163 disconnect_connections(conns) 164 end 165 end
Return an array of symbols for servers in the connection pool.
# File lib/sequel/connection_pool/sharded_threaded.rb 168 def servers 169 sync{@servers.keys} 170 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 180 def _size(server) 181 server = @servers[server] 182 @allocated[server].length + @available_connections[server].length 183 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 is 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 191 def acquire(thread, server) 192 if conn = assign_connection(thread, server) 193 return conn 194 end 195 196 timeout = @timeout 197 timer = Sequel.start_timer 198 199 sync do 200 @waiters[server].wait(@mutex, timeout) 201 if conn = next_available(server) 202 return(allocated(server)[thread] = conn) 203 end 204 end 205 206 until conn = assign_connection(thread, server) 207 elapsed = Sequel.elapsed_seconds_since(timer) 208 # :nocov: 209 raise_pool_timeout(elapsed, server) if elapsed > timeout 210 211 # It's difficult to get to this point, it can only happen if there is a race condition 212 # where a connection cannot be acquired even after the thread is signalled by the condition variable 213 sync do 214 @waiters[server].wait(@mutex, timeout - elapsed) 215 if conn = next_available(server) 216 return(allocated(server)[thread] = conn) 217 end 218 end 219 # :nocov: 220 end 221 222 conn 223 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 227 def assign_connection(thread, server) 228 alloc = nil 229 230 do_make_new = false 231 sync do 232 alloc = allocated(server) 233 if conn = next_available(server) 234 alloc[thread] = conn 235 return conn 236 end 237 238 if (n = _size(server)) >= (max = @max_size) 239 alloc.to_a.each do |t,c| 240 unless t.alive? 241 remove(t, c, server) 242 end 243 end 244 n = nil 245 end 246 247 if (n || _size(server)) < max 248 do_make_new = alloc[thread] = true 249 end 250 end 251 252 # Connect to the database outside of the connection pool mutex, 253 # as that can take a long time and the connection pool mutex 254 # shouldn't be locked while the connection takes place. 255 if do_make_new 256 begin 257 conn = make_new(server) 258 sync{alloc[thread] = conn} 259 ensure 260 unless conn 261 sync{alloc.delete(thread)} 262 end 263 end 264 end 265 266 conn 267 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 272 def checkin_connection(server, conn) 273 available_connections(server) << conn 274 @waiters[server].signal 275 conn 276 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 298 def disconnect_connections(conns) 299 conns.each{|conn| disconnect_connection(conn)} 300 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 282 def disconnect_server_connections(server) 283 remove_conns = allocated(server) 284 dis_conns = available_connections(server) 285 raise Sequel::Error, "invalid server: #{server}" unless remove_conns && dis_conns 286 287 @connections_to_remove.concat(remove_conns.values) 288 289 conns = dis_conns.dup 290 dis_conns.clear 291 @waiters[server].signal 292 conns 293 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 305 def next_available(server) 306 case @connection_handling 307 when :stack 308 available_connections(server).pop 309 else 310 available_connections(server).shift 311 end 312 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 316 def owned_connection(thread, server) 317 sync{@allocated[server][thread]} 318 end
If the server given is in the hash, return it, otherwise, return the default server.
# File lib/sequel/connection_pool/sharded_threaded.rb 321 def pick_server(server) 322 sync{@servers[server]} 323 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 327 def preconnect(concurrent = false) 328 conn_servers = @servers.keys.map!{|s| Array.new(max_size - _size(s), s)}.flatten! 329 330 if concurrent 331 conn_servers.map!{|s| Thread.new{[s, make_new(s)]}}.map!(&:value) 332 else 333 conn_servers.map!{|s| [s, make_new(s)]} 334 end 335 336 sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}} 337 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 341 def raise_pool_timeout(elapsed, server) 342 name = db.opts[:name] 343 raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}" 344 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 350 def release(thread, conn, server) 351 if @connections_to_remove.include?(conn) 352 remove(thread, conn, server) 353 else 354 conn = allocated(server).delete(thread) 355 356 if @connection_handling == :disconnect 357 @connections_to_disconnect << conn 358 else 359 checkin_connection(server, conn) 360 end 361 end 362 363 if waiter = @waiters[server] 364 waiter.signal 365 end 366 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 370 def remove(thread, conn, server) 371 @connections_to_remove.delete(conn) 372 allocated(server).delete(thread) if @servers.include?(server) 373 @connections_to_disconnect << conn 374 end