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   @waiters = {}
26 
27   add_servers([:default])
28   add_servers(opts[:servers].keys) if opts[:servers]
29 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
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
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
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
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
50 def allocated(server=:default)
51   @allocated[server]
52 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
75 def available_connections(server=:default)
76   @available_connections[server]
77 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
 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
freeze() click to toggle source
Calls superclass method
    # File lib/sequel/connection_pool/sharded_threaded.rb
104 def freeze
105   @servers.freeze
106   super
107 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
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
pool_type() click to toggle source
    # File lib/sequel/connection_pool/sharded_threaded.rb
170 def pool_type
171   :sharded_threaded
172 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
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
servers() click to toggle source

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
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
82 def size(server=:default)
83   @mutex.synchronize{_size(server)}
84 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
178 def _size(server)
179   server = @servers[server]
180   @allocated[server].length + @available_connections[server].length
181 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
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_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
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
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
270 def checkin_connection(server, conn)
271   available_connections(server) << conn
272   @waiters[server].signal
273   conn
274 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
294 def disconnect_connections(conns)
295   conns.each{|conn| disconnect_connection(conn)}
296 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
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
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
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
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
312 def owned_connection(thread, server)
313   sync{@allocated[server][thread]}
314 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
317 def pick_server(server)
318   sync{@servers[server]}
319 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
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_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
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
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
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
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
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