class Sequel::ShardedThreadedConnectionPool

  1. lib/sequel/connection_pool/sharded_threaded.rb
Superclass: ThreadedConnectionPool

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)

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   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)

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
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()

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
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)

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
54 def allocated(server=:default)
55   @allocated[server]
56 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
79 def available_connections(server=:default)
80   @available_connections[server]
81 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
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()
[show source] 
    # File lib/sequel/connection_pool/sharded_threaded.rb
106 def freeze
107   @servers.freeze
108   super
109 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(: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.

[show source] 
    # 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()
[show source] 
    # File lib/sequel/connection_pool/sharded_threaded.rb
173 def pool_type
174   :sharded_threaded
175 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
147 def remove_servers(servers)
148   conns = []
149   raise(Sequel::Error, "cannot remove default server") if servers.include?(:default)
150 
151   sync do
152     servers.each do |server|
153       if @servers.include?(server)
154         conns.concat(disconnect_server_connections(server))
155         @waiters.delete(server)
156         @available_connections.delete(server)
157         @allocated.delete(server)
158         @servers.delete(server)
159       end
160     end
161   end
162 
163   nil
164 ensure
165   disconnect_connections(conns)
166 end
servers()

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

[show source] 
    # File lib/sequel/connection_pool/sharded_threaded.rb
169 def servers
170   sync{@servers.keys}
171 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
86 def size(server=:default)
87   @mutex.synchronize{_size(server)}
88 end