class Sequel::ShardedThreadedConnectionPool

  1. lib/sequel/connection_pool/sharded_threaded.rb

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)

The following additional options are respected:


A hash of servers to use. Keys should be symbols. If not present, will use a single :default server.


The base hash to use for the servers. By default, Sequel uses 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.

[show source]
   # 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,
24   remove_instance_variable(:@waiter)
25   @waiters = {}
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.

[show source]
   # 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] =
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.

[show source]
   # File lib/sequel/connection_pool/sharded_threaded.rb
59 def all_connections
60   t = Sequel.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.

[show source]
   # 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.

[show source]
   # 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:


Should be a symbol specifing the server to disconnect from, or an array of symbols to specify multiple servers.

[show source]
    # 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     disconnect_connections(sync{disconnect_server_connections(s)})
 99   end
100 end
[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
102 def freeze
103   @servers.freeze
104   super
105 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.

[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
120 def hold(server=:default)
121   server = pick_server(server)
122   t = Sequel.current
123   if conn = owned_connection(t, server)
124     return yield(conn)
125   end
126   begin
127     conn = acquire(t, server)
128     yield conn
129   rescue Sequel::DatabaseDisconnectError, *@error_classes => e
130     sync{@connections_to_remove << conn} if conn && disconnect_error?(e)
131     raise
132   ensure
133     sync{release(t, conn, server)} if conn
134     while dconn = sync{@connections_to_disconnect.shift}
135       disconnect_connection(dconn)
136     end
137   end
138 end
[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
168 def pool_type
169   :sharded_threaded
170 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.

[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
143 def remove_servers(servers)
144   conns = nil
145   sync do
146     raise(Sequel::Error, "cannot remove default server") if servers.include?(:default)
147     servers.each do |server|
148       if @servers.include?(server)
149         conns = disconnect_server_connections(server)
150         @waiters.delete(server)
151         @available_connections.delete(server)
152         @allocated.delete(server)
153         @servers.delete(server)
154       end
155     end
156   end
158   if conns
159     disconnect_connections(conns)
160   end
161 end

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

[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
164 def servers
165   sync{@servers.keys}
166 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.

[show source]
   # File lib/sequel/connection_pool/sharded_threaded.rb
82 def size(server=:default)
83   @mutex.synchronize{_size(server)}
84 end