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)

Source

   # File lib/sequel/connection_pool/sharded_threaded.rb
20 def initialize(db, opts = OPTS)
21   super
22   @available_connections = {}
23   @connections_to_remove = []
24   @connections_to_disconnect = []
25   @servers = opts.fetch(:servers_hash, Hash.new(:default))
26   remove_instance_variable(:@waiter)
27   remove_instance_variable(:@allocated)
28   @allocated = {}
29   @waiters = {}
30 
31   add_servers([:default])
32   add_servers(opts[:servers].keys) if opts[:servers]
33 end

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

Public Instance Methods

add_servers (servers)

Source

   # File lib/sequel/connection_pool/sharded_threaded.rb
37 def add_servers(servers)
38   sync do
39     servers.each do |server|
40       unless @servers.has_key?(server)
41         @servers[server] = server
42         @available_connections[server] = []
43         allocated = {}
44         allocated.compare_by_identity
45         @allocated[server] = allocated
46         @waiters[server] = ConditionVariable.new
47       end
48     end
49   end
50 end

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.

all_connections () { |conn| ... }

Source

   # File lib/sequel/connection_pool/sharded_threaded.rb
65 def all_connections
66   t = Sequel.current
67   sync do
68     @allocated.values.each do |threads|
69       threads.each do |thread, conn|
70         yield conn if t == thread
71       end
72     end
73     @available_connections.values.each{|v| v.each{|c| yield c}}
74   end
75 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.

allocated (server=:default)

Source

   # File lib/sequel/connection_pool/sharded_threaded.rb
56 def allocated(server=:default)
57   @allocated[server]
58 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.

available_connections (server=:default)

Source

   # File lib/sequel/connection_pool/sharded_threaded.rb
81 def available_connections(server=:default)
82   @available_connections[server]
83 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.

disconnect (opts=OPTS)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
102 def disconnect(opts=OPTS)
103   (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |s|
104     disconnect_connections(sync{disconnect_server_connections(s)})
105   end
106 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 specifying the server to disconnect from, or an array of symbols to specify multiple servers.

freeze ()

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
108 def freeze
109   @servers.freeze
110   super
111 end

Calls superclass method

hold (server=:default) { |conn| ... }

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
126 def hold(server=:default)
127   server = pick_server(server)
128   t = Sequel.current
129   if conn = owned_connection(t, server)
130     return yield(conn)
131   end
132   begin
133     conn = acquire(t, server)
134     yield conn
135   rescue Sequel::DatabaseDisconnectError, *@error_classes => e
136     sync{@connections_to_remove << conn} if conn && disconnect_error?(e)
137     raise
138   ensure
139     sync{release(t, conn, server)} if conn
140     while dconn = sync{@connections_to_disconnect.shift}
141       disconnect_connection(dconn)
142     end
143   end
144 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.

pool_type ()

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
175 def pool_type
176   :sharded_threaded
177 end

remove_servers (servers)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
149 def remove_servers(servers)
150   conns = []
151   raise(Sequel::Error, "cannot remove default server") if servers.include?(:default)
152 
153   sync do
154     servers.each do |server|
155       if @servers.include?(server)
156         conns.concat(disconnect_server_connections(server))
157         @waiters.delete(server)
158         @available_connections.delete(server)
159         @allocated.delete(server)
160         @servers.delete(server)
161       end
162     end
163   end
164 
165   nil
166 ensure
167   disconnect_connections(conns)
168 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.

servers ()

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
171 def servers
172   sync{@servers.keys}
173 end

Return an array of symbols for servers in the connection pool.

size (server=:default)

Source

   # File lib/sequel/connection_pool/sharded_threaded.rb
88 def size(server=:default)
89   @mutex.synchronize{_size(server)}
90 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.

Private Instance Methods

_size (server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
183 def _size(server)
184   server = @servers[server]
185   @allocated[server].length + @available_connections[server].length
186 end

The total number of connections opened for the given server. The calling code should already have the mutex before calling this.

acquire (thread, server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
194 def acquire(thread, server)
195   if conn = assign_connection(thread, server)
196     return conn
197   end
198 
199   timeout = @timeout
200   timer = Sequel.start_timer
201 
202   if conn = acquire_available(thread, server, timeout)
203     return conn
204   end
205 
206   until conn = assign_connection(thread, server)
207     elapsed = Sequel.elapsed_seconds_since(timer)
208     # simplecov:disable
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     if conn = acquire_available(thread, server, timeout - elapsed)
214       return conn
215     end
216     # simplecov:enable
217   end
218 
219   conn
220 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.

acquire_available (thread, server, timeout)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
223 def acquire_available(thread, server, timeout)
224   sync do
225     # Check if connection was checked in between when assign_connection failed and now.
226     # This is very unlikely, but necessary to prevent a situation where the waiter
227     # will wait for a connection even though one has already been checked in.
228     # simplecov:disable
229     if conn = next_available(server)
230       return(allocated(server)[thread] = conn)
231     end
232     # simplecov:enable
233 
234     @waiters[server].wait(@mutex, timeout)
235 
236     # Connection still not available, could be because a connection was disconnected,
237     # may have to retry assign_connection to see if a new connection can be made.
238     if conn = next_available(server)
239       return(allocated(server)[thread] = conn)
240     end
241   end
242 end

Acquire a connection if one is already available, or waiting until it becomes available.

assign_connection (thread, server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
246 def assign_connection(thread, server)
247   alloc = nil
248 
249   do_make_new = false
250   sync do
251     alloc = allocated(server)
252     if conn = next_available(server)
253       alloc[thread] = conn
254       return conn
255     end
256 
257     if (n = _size(server)) >= (max = @max_size)
258       alloc.to_a.each do |t,c|
259         unless t.alive?
260           remove(t, c, server)
261         end
262       end
263       n = nil
264     end
265 
266     if (n || _size(server)) < max
267       do_make_new = alloc[thread] = true
268     end
269   end
270 
271   # Connect to the database outside of the connection pool mutex,
272   # as that can take a long time and the connection pool mutex
273   # shouldn't be locked while the connection takes place.
274   if do_make_new
275     begin
276       conn = make_new(server)
277       sync{alloc[thread] = conn}
278     ensure
279       unless conn
280         sync{alloc.delete(thread)}
281       end
282     end
283   end
284 
285   conn
286 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.

checkin_connection (server, conn)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
291 def checkin_connection(server, conn)
292   available_connections(server) << conn
293   @waiters[server].signal
294   conn
295 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.

disconnect_connections (conns)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
317 def disconnect_connections(conns)
318   conns.each{|conn| disconnect_connection(conn)}
319 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.

disconnect_server_connections (server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
301 def disconnect_server_connections(server)
302   remove_conns = allocated(server)
303   dis_conns = available_connections(server)
304   raise Sequel::Error, "invalid server: #{server}" unless remove_conns && dis_conns
305 
306   @connections_to_remove.concat(remove_conns.values)
307 
308   conns = dis_conns.dup
309   dis_conns.clear
310   @waiters[server].signal
311   conns
312 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.

next_available (server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
324 def next_available(server)
325   case @connection_handling
326   when :stack
327     available_connections(server).pop
328   else
329     available_connections(server).shift
330   end
331 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.

owned_connection (thread, server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
335 def owned_connection(thread, server)
336   sync{@allocated[server][thread]}
337 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.

pick_server (server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
340 def pick_server(server)
341   sync{@servers[server]}
342 end

If the server given is in the hash, return it, otherwise, return the default server.

preconnect (concurrent = false)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
346 def preconnect(concurrent = false)
347   conn_servers = sync{@servers.keys}.map!{|s| Array.new(max_size - _size(s), s)}.flatten!
348 
349   if concurrent
350     conn_servers.map!{|s| Thread.new{[s, make_new(s)]}}.map!(&:value)
351   else
352     conn_servers.map!{|s| [s, make_new(s)]}
353   end
354 
355   sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}}
356 end

Create the maximum number of connections immediately. The calling code should NOT have the mutex before calling this.

raise_pool_timeout (elapsed, server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
360 def raise_pool_timeout(elapsed, server)
361   name = db.opts[:name]
362   raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}"
363 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).

release (thread, conn, server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
369 def release(thread, conn, server)
370   if @connections_to_remove.include?(conn)
371     remove(thread, conn, server)
372   else
373     conn = allocated(server).delete(thread)
374 
375     if @connection_handling == :disconnect
376       @connections_to_disconnect << conn
377     else
378       checkin_connection(server, conn)
379     end
380   end
381 
382   if waiter = @waiters[server]
383     waiter.signal
384   end
385 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.

remove (thread, conn, server)

Source

    # File lib/sequel/connection_pool/sharded_threaded.rb
389 def remove(thread, conn, server)
390   @connections_to_remove.delete(conn)
391   allocated(server).delete(thread) if @servers.include?(server)
392   @connections_to_disconnect << conn
393 end

Removes the currently allocated connection from the connection pool. The calling code should already have the mutex before calling this.