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::CONNECTION_POOL_MAP, ConnectionPool::DEFAULT_SERVER, ConnectionPool::OPTS

Instance Attribute Summary

Attributes inherited from ThreadedConnectionPool

#max_size

Attributes inherited from ConnectionPool

#after_connect, #db

Instance Method Summary collapse

Methods inherited from ConnectionPool

#created_count

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 16

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

  if USE_WAITER
    @waiter = nil
    @waiters = {}
  end

  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. Primarily used in conjunction with master/slave or shard configurations. Allows for dynamic expansion of the potential slaves/shards at runtime. servers argument should be an array of symbols.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 34

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 if USE_WAITER
      end
    end
  end
end

#all_connectionsObject

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 = Thread.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.


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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.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 74

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)
  sync do
    (opts[:server] ? Array(opts[:server]) : @servers.keys).each do |s|
      disconnect_server(s)
    end
  end
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 118

def hold(server=:default)
  server = pick_server(server)
  t = Thread.current
  if conn = owned_connection(t, server)
    return yield(conn)
  end
  begin
    conn = acquire(t, server)
    yield conn
  rescue Sequel::DatabaseDisconnectError
    sync{@connections_to_remove << conn} if conn
    raise
  ensure
    sync{release(t, conn, server)} if conn
  end
end

#pool_typeObject


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 159

def pool_type
  :sharded_threaded
end

#remove_servers(servers) ⇒ Object

Remove servers from the connection pool. Primarily used in conjunction with master/slave or shard configurations. 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 139

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

#serversObject

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


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 155

def servers
  sync{@servers.keys}
end

#size(server = :default) ⇒ Object

The total number of connections opened for the given server, should be equal to available_connections.length + allocated.length. Nonexistent servers will return the created count of the default server.


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# File 'lib/sequel/connection_pool/sharded_threaded.rb', line 81

def size(server=:default)
  server = @servers[server]
  @allocated[server].length + @available_connections[server].length
end