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

new(db, opts = OPTS) click to toggle source

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.

Calls superclass method 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

add_servers(servers) click to toggle source

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
all_connections() { |conn| ... } click to toggle source

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
allocated(server=:default) click to toggle source

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
available_connections(server=:default) click to toggle source

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
disconnect(opts=OPTS) click to toggle source

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
freeze() click to toggle source
Calls superclass method
    # File lib/sequel/connection_pool/sharded_threaded.rb
106 def freeze
107   @servers.freeze
108   super
109 end
hold(server=:default) { |conn| ... } click to toggle source

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
pool_type() click to toggle source
    # File lib/sequel/connection_pool/sharded_threaded.rb
173 def pool_type
174   :sharded_threaded
175 end
remove_servers(servers) click to toggle source

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
servers() click to toggle source

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
size(server=:default) click to toggle source

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

_size(server) click to toggle source

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
acquire(thread, server) click to toggle source

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_connection(thread, server) click to toggle source

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
checkin_connection(server, conn) click to toggle source

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_connections(conns) click to toggle source

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
disconnect_server_connections(server) click to toggle source

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
next_available(server) click to toggle source

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
owned_connection(thread, server) click to toggle source

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
pick_server(server) click to toggle source

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
preconnect(concurrent = false) click to toggle source

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_pool_timeout(elapsed, server) click to toggle source

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
release(thread, conn, server) click to toggle source

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
remove(thread, conn, server) click to toggle source

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