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:

: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.

[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, 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)

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] = ConditionVariable.new
41       end
42     end
43   end
44 end
all_connections ()

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 = 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)

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
available_connections (server=:default)

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
disconnect (opts=OPTS)

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.

[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     if conns = sync{disconnect_server_connections(s)}
 99       disconnect_connections(conns)
100     end
101   end
102 end
freeze ()
[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
104 def freeze
105   @servers.freeze
106   super
107 end
hold (server=:default)

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
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 ()
[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
170 def pool_type
171   :sharded_threaded
172 end
remove_servers (servers)

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
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 ()

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

[show source]
    # File lib/sequel/connection_pool/sharded_threaded.rb
166 def servers
167   sync{@servers.keys}
168 end
size (server=:default)

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