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 replicas/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 59 def all_connections 60 t = Thread.current 61 sync do 62 @allocated.values.each do |threads| 63 threads.each do |thread, conn| 64 yield conn if t == thread 65 end 66 end 67 @available_connections.values.each{|v| v.each{|c| yield c}} 68 end 69 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 50 def allocated(server=:default) 51 @allocated[server] 52 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 75 def available_connections(server=:default) 76 @available_connections[server] 77 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 96 def disconnect(opts=OPTS) 97 (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |s| 98 if conns = sync{disconnect_server_connections(s)} 99 disconnect_connections(conns) 100 end 101 end 102 end
# File lib/sequel/connection_pool/sharded_threaded.rb 104 def freeze 105 @servers.freeze 106 super 107 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 122 def hold(server=:default) 123 server = pick_server(server) 124 t = Thread.current 125 if conn = owned_connection(t, server) 126 return yield(conn) 127 end 128 begin 129 conn = acquire(t, server) 130 yield conn 131 rescue Sequel::DatabaseDisconnectError, *@error_classes => e 132 sync{@connections_to_remove << conn} if conn && disconnect_error?(e) 133 raise 134 ensure 135 sync{release(t, conn, server)} if conn 136 while dconn = sync{@connections_to_disconnect.shift} 137 disconnect_connection(dconn) 138 end 139 end 140 end
# File lib/sequel/connection_pool/sharded_threaded.rb 170 def pool_type 171 :sharded_threaded 172 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 145 def remove_servers(servers) 146 conns = nil 147 sync do 148 raise(Sequel::Error, "cannot remove default server") if servers.include?(:default) 149 servers.each do |server| 150 if @servers.include?(server) 151 conns = disconnect_server_connections(server) 152 @waiters.delete(server) 153 @available_connections.delete(server) 154 @allocated.delete(server) 155 @servers.delete(server) 156 end 157 end 158 end 159 160 if conns 161 disconnect_connections(conns) 162 end 163 end
Return an array of symbols for servers in the connection pool.
# File lib/sequel/connection_pool/sharded_threaded.rb 166 def servers 167 sync{@servers.keys} 168 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 82 def size(server=:default) 83 @mutex.synchronize{_size(server)} 84 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 178 def _size(server) 179 server = @servers[server] 180 @allocated[server].length + @available_connections[server].length 181 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 189 def acquire(thread, server) 190 if conn = assign_connection(thread, server) 191 return conn 192 end 193 194 timeout = @timeout 195 timer = Sequel.start_timer 196 197 sync do 198 @waiters[server].wait(@mutex, timeout) 199 if conn = next_available(server) 200 return(allocated(server)[thread] = conn) 201 end 202 end 203 204 until conn = assign_connection(thread, server) 205 elapsed = Sequel.elapsed_seconds_since(timer) 206 raise_pool_timeout(elapsed, server) if elapsed > timeout 207 208 # :nocov: 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 sync do 212 @waiters[server].wait(@mutex, timeout - elapsed) 213 if conn = next_available(server) 214 return(allocated(server)[thread] = conn) 215 end 216 end 217 # :nocov: 218 end 219 220 conn 221 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 225 def assign_connection(thread, server) 226 alloc = nil 227 228 do_make_new = false 229 sync do 230 alloc = allocated(server) 231 if conn = next_available(server) 232 alloc[thread] = conn 233 return conn 234 end 235 236 if (n = _size(server)) >= (max = @max_size) 237 alloc.to_a.each do |t,c| 238 unless t.alive? 239 remove(t, c, server) 240 end 241 end 242 n = nil 243 end 244 245 if (n || _size(server)) < max 246 do_make_new = alloc[thread] = true 247 end 248 end 249 250 # Connect to the database outside of the connection pool mutex, 251 # as that can take a long time and the connection pool mutex 252 # shouldn't be locked while the connection takes place. 253 if do_make_new 254 begin 255 conn = make_new(server) 256 sync{alloc[thread] = conn} 257 ensure 258 unless conn 259 sync{alloc.delete(thread)} 260 end 261 end 262 end 263 264 conn 265 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 270 def checkin_connection(server, conn) 271 available_connections(server) << conn 272 @waiters[server].signal 273 conn 274 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 294 def disconnect_connections(conns) 295 conns.each{|conn| disconnect_connection(conn)} 296 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 280 def disconnect_server_connections(server) 281 @connections_to_remove.concat(allocated(server).values) 282 283 if dis_conns = available_connections(server) 284 conns = dis_conns.dup 285 dis_conns.clear 286 @waiters[server].signal 287 end 288 conns 289 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 301 def next_available(server) 302 case @connection_handling 303 when :stack 304 available_connections(server).pop 305 else 306 available_connections(server).shift 307 end 308 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 312 def owned_connection(thread, server) 313 sync{@allocated[server][thread]} 314 end
If the server given is in the hash, return it, otherwise, return the default server.
# File lib/sequel/connection_pool/sharded_threaded.rb 317 def pick_server(server) 318 sync{@servers[server]} 319 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 323 def preconnect(concurrent = false) 324 conn_servers = @servers.keys.map!{|s| Array.new(max_size - _size(s), s)}.flatten! 325 326 if concurrent 327 conn_servers.map!{|s| Thread.new{[s, make_new(s)]}}.map!(&:value) 328 else 329 conn_servers.map!{|s| [s, make_new(s)]} 330 end 331 332 sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}} 333 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 337 def raise_pool_timeout(elapsed, server) 338 name = db.opts[:name] 339 raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}" 340 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 346 def release(thread, conn, server) 347 if @connections_to_remove.include?(conn) 348 remove(thread, conn, server) 349 else 350 conn = allocated(server).delete(thread) 351 352 if @connection_handling == :disconnect 353 @connections_to_disconnect << conn 354 else 355 checkin_connection(server, conn) 356 end 357 end 358 359 if waiter = @waiters[server] 360 waiter.signal 361 end 362 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 366 def remove(thread, conn, server) 367 @connections_to_remove.delete(conn) 368 allocated(server).delete(thread) if @servers.include?(server) 369 @connections_to_disconnect << conn 370 end