class Sequel::ShardedThreadedConnectionPool

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) click to toggle source

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.

Calls superclass method Sequel::ThreadedConnectionPool.new
# File lib/sequel/connection_pool/sharded_threaded.rb, line 18
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

Public Instance Methods

add_servers(servers) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 36
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_connections() { |conn| ... } click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 61
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) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 52
def allocated(server=:default)
  @allocated[server]
end
available_connections(server=:default) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 76
def available_connections(server=:default)
  @available_connections[server]
end
disconnect(opts=OPTS) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 98
def disconnect(opts=OPTS)
  (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |s|
    if conns = sync{disconnect_server_connections(s)}
      disconnect_connections(conns)
    end
  end
end
freeze() click to toggle source
Calls superclass method
# File lib/sequel/connection_pool/sharded_threaded.rb, line 106
def freeze
  @servers.freeze
  super
end
hold(server=:default) { |conn| ... } click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 125
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, *@error_classes => e
    sync{@connections_to_remove << conn} if conn && disconnect_error?(e)
    raise
  ensure
    sync{release(t, conn, server)} if conn
  end
end
pool_type() click to toggle source
# File lib/sequel/connection_pool/sharded_threaded.rb, line 171
def pool_type
  :sharded_threaded
end
remove_servers(servers) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 146
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) if USE_WAITER
        @available_connections.delete(server)
        @allocated.delete(server)
        @servers.delete(server)
      end
    end
  end

  if conns
    disconnect_connections(conns)
  end
end
servers() click to toggle source

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

# File lib/sequel/connection_pool/sharded_threaded.rb, line 167
def servers
  sync{@servers.keys}
end
size(server=:default) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 83
def size(server=:default)
  server = @servers[server]
  @allocated[server].length + @available_connections[server].length
end

Private Instance Methods

_acquire(thread, server) click to toggle source

Assigns a connection to the supplied thread for the given server, if one is available. The calling code should already have the mutex when calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 180
def _acquire(thread, server)
  if conn = available(server)
    allocated(server)[thread] = conn
  end
end
acquire(thread, server) click to toggle source

Assigns a connection to the supplied thread, if one is available. The calling code should NOT already have the mutex when calling this.

This should return a connection is one is available within the timeout, or nil if a connection could not be acquired within the timeout.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 193
def acquire(thread, server)
  sync do
    if conn = _acquire(thread, server)
      return conn
    end

    time = Time.now
    @waiters[server].wait(@mutex, @timeout)
    Thread.pass

    until conn = _acquire(thread, server)
      deadline ||= time + @timeout
      current_time = Time.now
      raise_pool_timeout(current_time - time, server) if current_time > deadline
      # :nocov:
      # It's difficult to get to this point, it can only happen if there is a race condition
      # where a connection cannot be acquired even after the thread is signalled by the condition
      # variable that a connection is ready.
      @waiters[server].wait(@mutex, deadline - current_time)
      Thread.pass
      # :nocov:
    end

    conn
  end
end
available(server) click to toggle source

Returns an available connection to the given server. If no connection is available, tries to create a new connection. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 240
def available(server)
  next_available(server) || make_new(server)
end
checkin_connection(server, conn) click to toggle source

Return a connection to the pool of available connections for the server, returns the connection. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 247
def checkin_connection(server, conn)
  available_connections(server) << conn
  if USE_WAITER
    @waiters[server].signal
    Thread.pass
  end
  conn
end
disconnect_connections(conns) click to toggle source

Disconnect all given connections.

immediately, and schedules currently allocated connections for disconnection as soon as they are returned to the pool. The calling code should not have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 274
def disconnect_connections(conns)
  conns.each{|conn| disconnect_connection(conn)}
end
disconnect_server_connections(server) click to toggle source

Clear the array of available connections for the server, returning an array of previous available connections that should be disconnected (or nil if none should be). Mark any allocated connections to be removed when they are checked back in. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 260
def disconnect_server_connections(server)
  @connections_to_remove.concat(allocated(server).values)

  if dis_conns = available_connections(server)
    conns = dis_conns.dup
    dis_conns.clear
  end
  conns
end
make_new(server) click to toggle source

Creates a new connection to the given server if the size of the pool for the server is less than the maximum size of the pool. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 281
def make_new(server)
  if (n = size(server)) >= @max_size
    allocated(server).to_a.each{|t, c| release(t, c, server) unless t.alive?}
    n = nil
  end
  default_make_new(server) if (n || size(server)) < @max_size
end
next_available(server) click to toggle source

Return the next available connection in the pool for the given server, or nil if there is not currently an available connection for the server. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 292
def next_available(server)
  case @connection_handling
  when :stack
    available_connections(server).pop
  else
    available_connections(server).shift
  end
end
owned_connection(thread, server) click to toggle source

Returns the connection owned by the supplied thread for the given server, if any. The calling code should NOT already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 303
def owned_connection(thread, server)
  sync{@allocated[server][thread]}
end
pick_server(server) click to toggle source

If the server given is in the hash, return it, otherwise, return the default server.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 308
def pick_server(server)
  sync{@servers[server]}
end
preconnect(concurrent = false) click to toggle source

Create the maximum number of connections to each server immediately.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 313
def preconnect(concurrent = false)
  conn_servers = @servers.keys.map{|s| Array.new(max_size - size(s), s)}.flatten

  if concurrent
    conn_servers.map{|s| Thread.new{[s, make_new(s)]}}.map(&:join).each{|t| checkin_connection(*t.value)}
  else
    conn_servers.each{|s| checkin_connection(s, make_new(s))}
  end
end
raise_pool_timeout(elapsed, server) click to toggle source

Raise a PoolTimeout error showing the current timeout, the elapsed time, the server the connection attempt was made to, and the database's name (if any).

# File lib/sequel/connection_pool/sharded_threaded.rb, line 325
def raise_pool_timeout(elapsed, server)
  name = db.opts[:name]
  raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}"
end
release(thread, conn, server) click to toggle source

Releases the connection assigned to the supplied thread and server. If the server or connection given is scheduled for disconnection, remove the connection instead of releasing it back to the pool. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 334
def release(thread, conn, server)
  if @connections_to_remove.include?(conn)
    remove(thread, conn, server)
  else
    conn = allocated(server).delete(thread)

    if @connection_handling == :disconnect
      disconnect_connection(conn)
    else
      checkin_connection(server, conn)
    end
  end
end
remove(thread, conn, server) click to toggle source

Removes the currently allocated connection from the connection pool. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 350
def remove(thread, conn, server)
  @connections_to_remove.delete(conn)
  allocated(server).delete(thread) if @servers.include?(server)
  disconnect_connection(conn)
end