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 @waiters = {} 26 27 add_servers([:default]) 28 add_servers(opts[:servers].keys) if opts[:servers] 29 end
Public Instance Methods
Adds new servers to the connection pool. Allows for dynamic expansion of the potential slaves/shards at runtime. servers argument should be an array of symbols.
# File lib/sequel/connection_pool/sharded_threaded.rb 33 def add_servers(servers) 34 sync do 35 servers.each do |server| 36 unless @servers.has_key?(server) 37 @servers[server] = server 38 @available_connections[server] = [] 39 @allocated[server] = {} 40 @waiters[server] = ConditionVariable.new 41 end 42 end 43 end 44 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 58 def all_connections 59 t = Thread.current 60 sync do 61 @allocated.values.each do |threads| 62 threads.each do |thread, conn| 63 yield conn if t == thread 64 end 65 end 66 @available_connections.values.each{|v| v.each{|c| yield c}} 67 end 68 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 49 def allocated(server=:default) 50 @allocated[server] 51 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.
# File lib/sequel/connection_pool/sharded_threaded.rb 73 def available_connections(server=:default) 74 @available_connections[server] 75 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 94 def disconnect(opts=OPTS) 95 (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |s| 96 if conns = sync{disconnect_server_connections(s)} 97 disconnect_connections(conns) 98 end 99 end 100 end
# File lib/sequel/connection_pool/sharded_threaded.rb 102 def freeze 103 @servers.freeze 104 super 105 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 120 def hold(server=:default) 121 server = pick_server(server) 122 t = Thread.current 123 if conn = owned_connection(t, server) 124 return yield(conn) 125 end 126 begin 127 conn = acquire(t, server) 128 yield conn 129 rescue Sequel::DatabaseDisconnectError, *@error_classes => e 130 sync{@connections_to_remove << conn} if conn && disconnect_error?(e) 131 raise 132 ensure 133 sync{release(t, conn, server)} if conn 134 while dconn = sync{@connections_to_disconnect.shift} 135 disconnect_connection(dconn) 136 end 137 end 138 end
# File lib/sequel/connection_pool/sharded_threaded.rb 168 def pool_type 169 :sharded_threaded 170 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 143 def remove_servers(servers) 144 conns = nil 145 sync do 146 raise(Sequel::Error, "cannot remove default server") if servers.include?(:default) 147 servers.each do |server| 148 if @servers.include?(server) 149 conns = disconnect_server_connections(server) 150 @waiters.delete(server) 151 @available_connections.delete(server) 152 @allocated.delete(server) 153 @servers.delete(server) 154 end 155 end 156 end 157 158 if conns 159 disconnect_connections(conns) 160 end 161 end
Return an array of symbols for servers in the connection pool.
# File lib/sequel/connection_pool/sharded_threaded.rb 164 def servers 165 sync{@servers.keys} 166 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 80 def size(server=:default) 81 @mutex.synchronize{_size(server)} 82 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 176 def _size(server) 177 server = @servers[server] 178 @allocated[server].length + @available_connections[server].length 179 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 187 def acquire(thread, server) 188 if conn = assign_connection(thread, server) 189 return conn 190 end 191 192 timeout = @timeout 193 timer = Sequel.start_timer 194 195 sync do 196 @waiters[server].wait(@mutex, timeout) 197 if conn = next_available(server) 198 return(allocated(server)[thread] = conn) 199 end 200 end 201 202 until conn = assign_connection(thread, server) 203 elapsed = Sequel.elapsed_seconds_since(timer) 204 raise_pool_timeout(elapsed, server) if elapsed > timeout 205 206 # :nocov: 207 # It's difficult to get to this point, it can only happen if there is a race condition 208 # where a connection cannot be acquired even after the thread is signalled by the condition variable 209 sync do 210 @waiters[server].wait(@mutex, timeout - elapsed) 211 if conn = next_available(server) 212 return(allocated(server)[thread] = conn) 213 end 214 end 215 # :nocov: 216 end 217 218 conn 219 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 223 def assign_connection(thread, server) 224 alloc = allocated(server) 225 226 do_make_new = false 227 sync do 228 if conn = next_available(server) 229 alloc[thread] = conn 230 return conn 231 end 232 233 if (n = _size(server)) >= (max = @max_size) 234 alloc.to_a.each do |t,c| 235 unless t.alive? 236 remove(t, c, server) 237 end 238 end 239 n = nil 240 end 241 242 if (n || _size(server)) < max 243 do_make_new = alloc[thread] = true 244 end 245 end 246 247 # Connect to the database outside of the connection pool mutex, 248 # as that can take a long time and the connection pool mutex 249 # shouldn't be locked while the connection takes place. 250 if do_make_new 251 begin 252 conn = make_new(server) 253 sync{alloc[thread] = conn} 254 ensure 255 unless conn 256 sync{alloc.delete(thread)} 257 end 258 end 259 end 260 261 conn 262 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 267 def checkin_connection(server, conn) 268 available_connections(server) << conn 269 @waiters[server].signal 270 conn 271 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 291 def disconnect_connections(conns) 292 conns.each{|conn| disconnect_connection(conn)} 293 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 277 def disconnect_server_connections(server) 278 @connections_to_remove.concat(allocated(server).values) 279 280 if dis_conns = available_connections(server) 281 conns = dis_conns.dup 282 dis_conns.clear 283 @waiters[server].signal 284 end 285 conns 286 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 298 def next_available(server) 299 case @connection_handling 300 when :stack 301 available_connections(server).pop 302 else 303 available_connections(server).shift 304 end 305 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 309 def owned_connection(thread, server) 310 sync{@allocated[server][thread]} 311 end
If the server given is in the hash, return it, otherwise, return the default server.
# File lib/sequel/connection_pool/sharded_threaded.rb 314 def pick_server(server) 315 sync{@servers[server]} 316 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 320 def preconnect(concurrent = false) 321 conn_servers = @servers.keys.map!{|s| Array.new(max_size - _size(s), s)}.flatten! 322 323 if concurrent 324 conn_servers.map!{|s| Thread.new{[s, make_new(s)]}}.map!(&:value) 325 else 326 conn_servers.map!{|s| [s, make_new(s)]} 327 end 328 329 sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}} 330 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 334 def raise_pool_timeout(elapsed, server) 335 name = db.opts[:name] 336 raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}" 337 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 343 def release(thread, conn, server) 344 if @connections_to_remove.include?(conn) 345 remove(thread, conn, server) 346 else 347 conn = allocated(server).delete(thread) 348 349 if @connection_handling == :disconnect 350 @connections_to_disconnect << conn 351 else 352 checkin_connection(server, conn) 353 end 354 end 355 356 if waiter = @waiters[server] 357 waiter.signal 358 end 359 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 363 def remove(thread, conn, server) 364 @connections_to_remove.delete(conn) 365 allocated(server).delete(thread) if @servers.include?(server) 366 @connections_to_disconnect << conn 367 end