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

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 {|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
172 def pool_type
173   :sharded_threaded
174 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 = 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
servers() click to toggle source

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
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
180 def _size(server)
181   server = @servers[server]
182   @allocated[server].length + @available_connections[server].length
183 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 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_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
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
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
272 def checkin_connection(server, conn)
273   available_connections(server) << conn
274   @waiters[server].signal
275   conn
276 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
298 def disconnect_connections(conns)
299   conns.each{|conn| disconnect_connection(conn)}
300 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
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
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
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
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
316 def owned_connection(thread, server)
317   sync{@allocated[server][thread]}
318 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
321 def pick_server(server)
322   sync{@servers[server]}
323 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
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_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
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
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
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
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
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