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 17
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

Public Instance Methods

add_servers(servers) click to toggle source

Adds new servers to the connection pool. 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 32
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() { |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 57
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 48
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 72
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 93
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 101
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 119
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
    while dconn = sync{@connections_to_disconnect.shift}
      disconnect_connection(dconn)
    end
  end
end
pool_type() click to toggle source
# File lib/sequel/connection_pool/sharded_threaded.rb, line 167
def pool_type
  :sharded_threaded
end
remove_servers(servers) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 142
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() click to toggle source

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

# File lib/sequel/connection_pool/sharded_threaded.rb, line 163
def servers
  sync{@servers.keys}
end
size(server=:default) click to toggle source

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.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 79
def size(server=:default)
  @mutex.synchronize{_size(server)}
end

Private Instance Methods

_size(server) click to toggle source

The total number of connections opened for the given server. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 175
def _size(server)
  server = @servers[server]
  @allocated[server].length + @available_connections[server].length
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 186
def acquire(thread, server)
  if conn = assign_connection(thread, server)
    return conn
  end

  timeout = @timeout
  timer = Sequel.start_timer

  sync do
    @waiters[server].wait(@mutex, timeout)
    if conn = next_available(server)
      return(allocated(server)[thread] = conn)
    end
  end

  until conn = assign_connection(thread, server)
    elapsed = Sequel.elapsed_seconds_since(timer)
    raise_pool_timeout(elapsed, server) if elapsed > timeout

    # :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
    sync do
      @waiters[server].wait(@mutex, timeout - elapsed)
      if conn = next_available(server)
        return(allocated(server)[thread] = conn)
      end
    end
    # :nocov:
  end

  conn
end
assign_connection(thread, server) click to toggle source

Assign a connection to the thread, or return nil if one cannot be assigned. The caller should NOT have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 222
def assign_connection(thread, server)
  alloc = allocated(server)

  do_make_new = false
  sync do
    if conn = next_available(server)
      alloc[thread] = conn
      return conn
    end

    if (n = _size(server)) >= (max = @max_size)
      alloc.to_a.each do |t,c|
        unless t.alive?
          remove(t, c, server)
        end
      end
      n = nil
    end

    if (n || _size(server)) < max
      do_make_new = alloc[thread] = true
    end
  end

  # Connect to the database outside of the connection pool mutex,
  # as that can take a long time and the connection pool mutex
  # shouldn't be locked while the connection takes place.
  if do_make_new
    begin
      conn = make_new(server)
      sync{alloc[thread] = conn}
    ensure
      unless conn
        sync{alloc.delete(thread)}
      end
    end
  end

  conn
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 266
def checkin_connection(server, conn)
  available_connections(server) << conn
  @waiters[server].signal
  conn
end
disconnect_connections(conns) click to toggle source

Disconnect all available connections immediately, and schedule 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 290
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 276
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
    @waiters[server].signal
  end
  conns
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 297
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 308
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 313
def pick_server(server)
  sync{@servers[server]}
end
preconnect(concurrent = false) click to toggle source

Create the maximum number of connections immediately. The calling code should NOT have the mutex before calling this.

# File lib/sequel/connection_pool/sharded_threaded.rb, line 319
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!(&:value)
  else
    conn_servers.map!{|s| [s, make_new(s)]}
  end

  sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}}
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 333
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 342
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
      @connections_to_disconnect << conn
    else
      checkin_connection(server, conn)
    end
  end

  if waiter = @waiters[server]
    waiter.signal
  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 362
def remove(thread, conn, server)
  @connections_to_remove.delete(conn)
  allocated(server).delete(thread) if @servers.include?(server)
  @connections_to_disconnect << conn
end