Class: Sequel::ShardedThreadedConnectionPool

Inherits:
ThreadedConnectionPool show all
Defined in:
lib/sequel/connection_pool/sharded_threaded.rb

Overview

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.

Constant Summary

Constants inherited from ThreadedConnectionPool

ThreadedConnectionPool::USE_WAITER

Constants inherited from ConnectionPool

ConnectionPool::OPTS, ConnectionPool::POOL_CLASS_MAP

Instance Attribute Summary

Attributes inherited from ThreadedConnectionPool

#max_size

Attributes inherited from ConnectionPool

#after_connect, #connect_sqls, #db

Instance Method Summary collapse

Methods included from ConnectionPool::ClassMethods

#get_pool

Constructor Details

#initialize(db, opts = OPTS) ⇒ ShardedThreadedConnectionPool

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 18

def initialize(db, opts = OPTS)
  super
  @available_connections = {}
  @connections_to_remove = []
  @connections_to_disconnect = []
  @servers = opts.fetch(:servers_hash, Hash.new(:default))
  remove_instance_variable(:@waiter)
  @waiters = {}

  add_servers([:default])
  add_servers(opts[:servers].keys) if opts[:servers]
end

Instance Method Details

#add_servers(servers) ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 33

def add_servers(servers)
  sync do
    servers.each do |server|
      unless @servers.has_key?(server)
        @servers[server] = server
        @available_connections[server] = []
        @allocated[server] = {}
        @waiters[server] = ConditionVariable.new
      end
    end
  end
end

#all_connections ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 59

def all_connections
  t = Sequel.current
  sync do
    @allocated.values.each do |threads|
      threads.each do |thread, conn|
        yield conn if t == thread
      end
    end
    @available_connections.values.each{|v| v.each{|c| yield c}}
  end
end

#allocated(server = :default) ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 50

def allocated(server=:default)
  @allocated[server]
end

#available_connections(server = :default) ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 75

def available_connections(server=:default)
  @available_connections[server]
end

#disconnect(opts = OPTS) ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 96

def disconnect(opts=OPTS)
  (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |s|
    disconnect_connections(sync{disconnect_server_connections(s)})
  end
end

#freeze ⇒ Object 


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 102

def freeze
  @servers.freeze
  super
end

#hold(server = :default) ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 120

def hold(server=:default)
  server = pick_server(server)
  t = Sequel.current
  if conn = owned_connection(t, server)
    return yield(conn)
  end
  begin
    conn = acquire(t, server)
    yield conn
  rescue Sequel::DatabaseDisconnectError, *@error_classes => e
    sync{@connections_to_remove << conn} if conn && disconnect_error?(e)
    raise
  ensure
    sync{release(t, conn, server)} if conn
    while dconn = sync{@connections_to_disconnect.shift}
      disconnect_connection(dconn)
    end
  end
end

#pool_type ⇒ Object 


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 168

def pool_type
  :sharded_threaded
end

#remove_servers(servers) ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 143

def remove_servers(servers)
  conns = nil
  sync do
    raise(Sequel::Error, "cannot remove default server") if servers.include?(:default)
    servers.each do |server|
      if @servers.include?(server)
        conns = disconnect_server_connections(server)
        @waiters.delete(server)
        @available_connections.delete(server)
        @allocated.delete(server)
        @servers.delete(server)
      end
    end
  end

  if conns
    disconnect_connections(conns)
  end
end

#servers ⇒ Object

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


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 164

def servers
  sync{@servers.keys}
end

#size(server = :default) ⇒ Object

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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 82

def size(server=:default)
  @mutex.synchronize{_size(server)}
end