Class: ActiveRecord::ConnectionAdapters::ConnectionPool

Relationships & Source Files
Namespace Children
Modules: `BiasableQueue`, `ExecutorHooks`
Classes: `ConnectionLeasingQueue`, `Lease`, `LeaseRegistry`, `Queue`, `Reaper`, `WeakThreadKeyMap`
Super Chains via Extension / Inclusion / Inheritance
Instance Chain: self, `AbstractPool`, `QueryCache::ConnectionPoolConfiguration`, MonitorMixin
Inherits:	Object
Defined in:	activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, activerecord/lib/active_record/connection_adapters/abstract/connection_pool/reaper.rb

Overview

Active Record Connection Pool

Connection pool base class for managing Active Record database connections.

Introduction

A connection pool synchronizes thread access to a limited number of database connections. The basic idea is that each thread checks out a database connection from the pool, uses that connection, and checks the connection back in. ConnectionPool is completely thread-safe, and will ensure that a connection cannot be used by two threads at the same time, as long as ConnectionPool’s contract is correctly followed. It will also handle cases in which there are more threads than connections: if all connections have been checked out, and a thread tries to checkout a connection anyway, then ConnectionPool will wait until some other thread has checked in a connection, or the #checkout_timeout has expired.

Obtaining (checking out) a connection

Connections can be obtained and used from a connection pool in several ways:

Simply use {ActiveRecord::Base.lease_connection}. When you’re done with the connection(s) and wish it to be returned to the pool, you call ActiveRecord::Base.connection_handler.clear_active_connections!. This is the default behavior for Active Record when used in conjunction with Action Pack’s request handling cycle.
Manually check out a connection from the pool with ActiveRecord::Base.connection_pool.checkout. You are responsible for returning this connection to the pool when finished by calling ActiveRecord::Base.connection_pool.checkin(connection).
Use {ActiveRecord::Base.connection_pool.with_connection(&block)}, which obtains a connection, yields it as the sole argument to the block, and returns it to the pool after the block completes.

Connections in the pool are actually AbstractAdapter objects (or objects compatible with AbstractAdapter’s interface).

While a thread has a connection checked out from the pool using one of the above three methods, that connection will automatically be the one used by ::ActiveRecord queries executing on that thread. It is not required to explicitly pass the checked out connection to Rails models or queries, for example.

Options

There are several connection-pooling-related options that you can add to your database connection configuration:

pool: maximum number of connections the pool may manage (default 5).
idle_timeout: number of seconds that a connection will be kept unused in the pool before it is automatically disconnected (default 300 seconds). Set this to zero to keep connections forever.
#checkout_timeout: number of seconds to wait for a connection to become available before giving up and raising a timeout error (default 5 seconds).

Class Method Summary

.install_executor_hooks(executor = ActiveSupport::Executor)
.new(pool_config) ⇒ ConnectionPool constructor

Creates a new ConnectionPool object.

Instance Attribute Summary

#async_executor readonly
#automatic_reconnect rw
#checkout_timeout rw
#connected? ⇒ Boolean readonly

Returns true if a connection has already been opened.
#db_config readonly
#pool_config readonly
#reaper readonly
#role readonly
#schema_reflection rw
#schema_reflection=(schema_reflection) rw
#server_version readonly
#shard readonly
#size readonly
#active_connection readonly Internal use only

Alias for #active_connection?.
#discarded? ⇒ Boolean readonly Internal use only
#permanent_lease? ⇒ Boolean readonly Internal use only

Instance Method Summary

#active_connection? ⇒ Boolean (also: #active_connection) readonly

Returns true if there is an open connection being used for the current thread.
#checkin(conn)

Check-in a database connection back into the pool, indicating that you no longer need this connection.
#checkout(checkout_timeout = @checkout_timeout)

Check-out a database connection from the pool, indicating that you want to use it.
#clear_reloadable_connections(raise_on_acquisition_timeout = true)

Clears the cache which maps classes and re-connects connections that require reloading.
#clear_reloadable_connections!

Clears the cache which maps classes and re-connects connections that require reloading.
#connections

Returns an array containing the connections currently in the pool.
#disconnect(raise_on_acquisition_timeout = true)

Disconnects all connections in the pool, and clears the pool.
#disconnect!

Disconnects all connections in the pool, and clears the pool.
#flush(minimum_idle = @idle_timeout)

Disconnect all connections that have been idle for at least minimum_idle seconds.
#flush!

Disconnect all currently idle connections.
#lease_connection

Retrieve the connection associated with the current thread, or call #checkout to obtain one if necessary.
#reap

Recover lost connections for the pool.
#release_connection(existing_lease = nil)

Signal that the thread is finished with the current connection.
#remove(conn)

Remove a connection from the connection pool.
#schema_cache
#stat

Returns the connection pool’s usage statistic.
#with_connection(prevent_permanent_checkout: false)

Yields a connection from the connection pool to the block.
#acquire_connection(checkout_timeout) private

Acquire a connection by one of 1) immediately removing one from the queue of available connections, 2) creating a new connection if the pool is not at capacity, 3) waiting on the queue for a connection to become available.
#adopt_connection(conn) private
#attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout = true) private
#build_async_executor private
#bulk_make_new_connections(num_new_conns_needed) private
#checkout_and_verify(c) private
#checkout_for_exclusive_access(checkout_timeout) private
#checkout_new_connection private
#connection_lease private
#new_connection private
#release(conn, owner_thread = conn.owner) private

Alias for #remove_connection_from_thread_cache.
#remove_connection_from_thread_cache(conn, owner_thread = conn.owner) (also: #release) private
#try_to_checkout_new_connection private

If the pool is not at a @size limit, establish new connection.
#with_exclusively_acquired_all_connections(raise_on_acquisition_timeout = true) private

Take control of all existing connections so a “group” action such as reload/disconnect can be performed safely.
#with_new_connections_blocked private
#connection_class Internal use only
#discard! Internal use only

Discards all connections in the pool (even if they’re currently leased!), along with the pool itself.
#inspect Internal use only
#internal_metadata Internal use only
#migration_context Internal use only
#migrations_paths Internal use only
#num_waiting_in_queue Internal use only
#pin_connection!(lock_thread) Internal use only
#schedule_query(future_result) Internal use only
#schema_migration Internal use only
#unpin_connection! Internal use only

`QueryCache::ConnectionPoolConfiguration` - Included

#checkout_and_verify, #clear_query_cache, #dirties_query_cache,
#disable_query_cache	Disable the query cache within the block.
#disable_query_cache!, #enable_query_cache, #enable_query_cache!, #initialize, #query_cache, #query_cache_enabled

Constructor Details

.new(pool_config) ⇒ `ConnectionPool`

Creates a new ConnectionPool object. #pool_config is a PoolConfig object which describes database connection information (e.g. adapter, host name, username, password, etc), as well as the maximum size for this ConnectionPool.

The default ConnectionPool maximum size is 5.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 226


def initialize(pool_config)
  super()

  @pool_config = pool_config
  @db_config = pool_config.db_config
  @role = pool_config.role
  @shard = pool_config.shard

  @checkout_timeout = db_config.checkout_timeout
  @idle_timeout = db_config.idle_timeout
  @size = db_config.pool

  # This variable tracks the cache of threads mapped to reserved connections, with the
  # sole purpose of speeding up the connection method. It is not the authoritative
  # registry of which thread owns which connection. Connection ownership is tracked by
  # the connection.owner attr on each connection instance.
  # The invariant works like this: if there is mapping of <tt>thread => conn</tt>,
  # then that thread does indeed own that conn. However, an absence of such
  # mapping does not mean that the thread doesn't own the said connection. In
  # that case conn.owner attr should be consulted.
  # Access and modification of <tt>@leases</tt> does not require
  # synchronization.
  @leases = LeaseRegistry.new

  @connections         = []
  @automatic_reconnect = true

  # Connection pool allows for concurrent (outside the main synchronize section)
  # establishment of new connections. This variable tracks the number of threads
  # currently in the process of independently establishing connections to the DB.
  @now_connecting = 0

  @threads_blocking_new_connections = 0

  @available = ConnectionLeasingQueue.new self
  @pinned_connection = nil
  @pinned_connections_depth = 0

  @async_executor = build_async_executor

  @schema_cache = nil

  @reaper = Reaper.new(self, db_config.reaping_frequency)
  @reaper.run
end

Class Method Details

.install_executor_hooks(executor = ActiveSupport::Executor)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 206


def install_executor_hooks(executor = ActiveSupport::Executor)
  executor.register_hook(ExecutorHooks)
end

Instance Attribute Details

#active_connection (readonly)

This method is for internal use only.

Alias for #active_connection?.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 373


alias_method :active_connection, :active_connection? # :nodoc:

#async_executor (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216


attr_reader :db_config, :size, :reaper, :pool_config, :async_executor, :role, :shard

#automatic_reconnect (rw)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 215


attr_accessor :automatic_reconnect, :checkout_timeout

#checkout_timeout (rw)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 215


attr_accessor :automatic_reconnect, :checkout_timeout

#connected? ⇒ `Boolean` (readonly)

Returns true if a connection has already been opened.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 421


def connected?
  synchronize { @connections.any?(&:connected?) }
end

#db_config (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216


attr_reader :db_config, :size, :reaper, :pool_config, :async_executor, :role, :shard

#discarded? ⇒ `Boolean` (readonly)

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 488


def discarded? # :nodoc:
  @connections.nil?
end

#permanent_lease? ⇒ `Boolean` (readonly)

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 315


def permanent_lease? # :nodoc:
  connection_lease.sticky.nil?
end

#pool_config (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216


attr_reader :db_config, :size, :reaper, :pool_config, :async_executor, :role, :shard

#reaper (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216


attr_reader :db_config, :size, :reaper, :pool_config, :async_executor, :role, :shard

#role (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216


attr_reader :db_config, :size, :reaper, :pool_config, :async_executor, :role, :shard

#schema_reflection (rw)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 218


delegate :schema_reflection, :server_version, to: :pool_config

#schema_reflection=(schema_reflection) (rw)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 283


def schema_reflection=(schema_reflection)
  pool_config.schema_reflection = schema_reflection
  @schema_cache = nil
end

#server_version (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 218


delegate :schema_reflection, :server_version, to: :pool_config

#shard (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216


attr_reader :db_config, :size, :reaper, :pool_config, :async_executor, :role, :shard

#size (readonly)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216


attr_reader :db_config, :size, :reaper, :pool_config, :async_executor, :role, :shard

Instance Method Details

#acquire_connection(checkout_timeout) (private)

Acquire a connection by one of 1) immediately removing one from the queue of available connections, 2) creating a new connection if the pool is not at capacity, 3) waiting on the queue for a connection to become available.

Raises:

::ActiveRecord::ConnectionTimeoutError if a connection could not be acquired

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 843


def acquire_connection(checkout_timeout)
  # NOTE: we rely on <tt>@available.poll</tt> and try_to_checkout_new_connection to
  # conn.lease the returned connection (and to do this in a synchronized
  # section). This is not the cleanest implementation, as ideally we would
  # <tt>synchronize { conn.lease }</tt> in this method, but by leaving it to <tt>@available.poll</tt>
  # and try_to_checkout_new_connection we can piggyback on synchronize sections
  # of the said methods and avoid an additional synchronize overhead.
  if conn = @available.poll || try_to_checkout_new_connection
    conn
  else
    reap
    # Retry after reaping, which may return an available connection,
    # remove an inactive connection, or both
    if conn = @available.poll || try_to_checkout_new_connection
      conn
    else
      @available.poll(checkout_timeout)
    end
  end
rescue ConnectionTimeoutError => ex
  raise ex.set_pool(self)
end

#active_connection? ⇒ `Boolean` (readonly) Also known as: #active_connection

Returns true if there is an open connection being used for the current thread.

This method only works for connections that have been obtained through #lease_connection or #with_connection methods. Connections obtained through #checkout will not be detected by #active_connection?

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 370


def active_connection?
  connection_lease.connection
end

#adopt_connection(conn) (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 913


def adopt_connection(conn)
  conn.pool = self
  @connections << conn

  # We just created the first connection, it's time to load the schema
  # cache if that wasn't eagerly done before
  if @schema_cache.nil? && ActiveRecord.lazily_load_schema_cache
    schema_cache.load!
  end
end

#attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout = true) (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 734


def attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout = true)
  collected_conns = synchronize do
    reap # No need to wait for dead owners

    # account for our own connections
    @connections.select { |conn| conn.owner == ActiveSupport::IsolatedExecutionState.context }
  end

  newly_checked_out = []
  timeout_time      = Process.clock_gettime(Process::CLOCK_MONOTONIC) + (@checkout_timeout * 2)

  @available.with_a_bias_for(ActiveSupport::IsolatedExecutionState.context) do
    loop do
      synchronize do
        return if collected_conns.size == @connections.size && @now_connecting == 0

        remaining_timeout = timeout_time - Process.clock_gettime(Process::CLOCK_MONOTONIC)
        remaining_timeout = 0 if remaining_timeout < 0
        conn = checkout_for_exclusive_access(remaining_timeout)
        collected_conns   << conn
        newly_checked_out << conn
      end
    end
  end
rescue ExclusiveConnectionTimeoutError
  # <tt>raise_on_acquisition_timeout == false</tt> means we are directed to ignore any
  # timeouts and are expected to just give up: we've obtained as many connections
  # as possible, note that in a case like that we don't return any of the
  # newly_checked_out connections.

  if raise_on_acquisition_timeout
    release_newly_checked_out = true
    raise
  end
rescue Exception # if something else went wrong
  # this can't be a "naked" rescue, because we have should return conns
  # even for non-StandardErrors
  release_newly_checked_out = true
  raise
ensure
  if release_newly_checked_out && newly_checked_out
    # releasing only those conns that were checked out in this method, conns
    # checked outside this method (before it was called) are not for us to release
    newly_checked_out.each { |conn| checkin(conn) }
  end
end

#build_async_executor (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 695


def build_async_executor
  case ActiveRecord.async_query_executor
  when :multi_thread_pool
    if @db_config.max_threads > 0
      Concurrent::ThreadPoolExecutor.new(
        min_threads: @db_config.min_threads,
        max_threads: @db_config.max_threads,
        max_queue: @db_config.max_queue,
        fallback_policy: :caller_runs
      )
    end
  when :global_thread_pool
    ActiveRecord.global_thread_pool_async_query_executor
  end
end

#bulk_make_new_connections(num_new_conns_needed) (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 713


def bulk_make_new_connections(num_new_conns_needed)
  num_new_conns_needed.times do
    # try_to_checkout_new_connection will not exceed pool's @size limit
    if new_conn = try_to_checkout_new_connection
      # make the new_conn available to the starving threads stuck @available Queue
      checkin(new_conn)
    end
  end
end

#checkin(conn)

Check-in a database connection back into the pool, indicating that you no longer need this connection.

conn: an AbstractAdapter object, which was obtained by earlier by calling #checkout on this pool.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 564


def checkin(conn)
  return if @pinned_connection.equal?(conn)

  conn.lock.synchronize do
    synchronize do
      connection_lease.clear(conn)

      conn._run_checkin_callbacks do
        conn.expire
      end

      @available.add conn
    end
  end
end

#checkout(checkout_timeout = @checkout_timeout)

Check-out a database connection from the pool, indicating that you want to use it. You should call #checkin when you no longer need this.

This is done by either returning and leasing existing connection, or by creating a new connection and leasing it.

If all connections are leased and the pool is at capacity (meaning the number of currently leased connections is greater than or equal to the size limit set), an ::ActiveRecord::ConnectionTimeoutError exception will be raised.

Returns: an AbstractAdapter object.

Raises:

::ActiveRecord::ConnectionTimeoutError no connection can be obtained from the pool.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 541


def checkout(checkout_timeout = @checkout_timeout)
  if @pinned_connection
    @pinned_connection.lock.synchronize do
      synchronize do
        @pinned_connection.verify!
        # Any leased connection must be in @connections otherwise
        # some methods like #connected? won't behave correctly
        unless @connections.include?(@pinned_connection)
          @connections << @pinned_connection
        end
      end
    end
    @pinned_connection
  else
    checkout_and_verify(acquire_connection(checkout_timeout))
  end
end

#checkout_and_verify(c) (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 929


def checkout_and_verify(c)
  c._run_checkout_callbacks do
    c.clean!
  end
  c
rescue Exception
  remove c
  c.disconnect!
  raise
end

#checkout_for_exclusive_access(checkout_timeout) (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 783


def checkout_for_exclusive_access(checkout_timeout)
  checkout(checkout_timeout)
rescue ConnectionTimeoutError
  # this block can't be easily moved into attempt_to_checkout_all_existing_connections's
  # rescue block, because doing so would put it outside of synchronize section, without
  # being in a critical section thread_report might become inaccurate
  msg = +"could not obtain ownership of all database connections in #{checkout_timeout} seconds"

  thread_report = []
  @connections.each do |conn|
    unless conn.owner == ActiveSupport::IsolatedExecutionState.context
      thread_report << "#{conn} is owned by #{conn.owner}"
    end
  end

  msg << " (#{thread_report.join(', ')})" if thread_report.any?

  raise ExclusiveConnectionTimeoutError.new(msg, connection_pool: self)
end

#checkout_new_connection (private)

Raises:

(ConnectionNotEstablished)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 924


def checkout_new_connection
  raise ConnectionNotEstablished unless @automatic_reconnect
  new_connection
end

#clear_reloadable_connections(raise_on_acquisition_timeout = true)

Clears the cache which maps classes and re-connects connections that require reloading.

Raises:

::ActiveRecord::ExclusiveConnectionTimeoutError if unable to gain ownership of all connections in the pool within a timeout interval (default duration is spec.db_config.checkout_timeout * 2 seconds).

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 499


def clear_reloadable_connections(raise_on_acquisition_timeout = true)
  with_exclusively_acquired_all_connections(raise_on_acquisition_timeout) do
    synchronize do
      @connections.each do |conn|
        if conn.in_use?
          conn.steal!
          checkin conn
        end
        conn.disconnect! if conn.requires_reloading?
      end
      @connections.delete_if(&:requires_reloading?)
      @available.clear
    end
  end
end

#clear_reloadable_connections!

Clears the cache which maps classes and re-connects connections that require reloading.

The pool first tries to gain ownership of all connections. If unable to do so within a timeout interval (default duration is spec.db_config.checkout_timeout * 2 seconds), then the pool forcefully clears the cache and reloads connections without any regard for other connection owning threads.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 523


def clear_reloadable_connections!
  clear_reloadable_connections(false)
end

#connection_class

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 361


def connection_class # :nodoc:
  pool_config.connection_class
end

#connection_lease (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 691


def connection_lease
  @leases[ActiveSupport::IsolatedExecutionState.context]
end

#connections

Returns an array containing the connections currently in the pool. Access to the array does not require synchronization on the pool because the array is newly created and not retained by the pool.

However; this method bypasses the ConnectionPool’s thread-safe connection access pattern. A returned connection may be owned by another thread, unowned, or by happen-stance owned by the calling thread.

Calling methods on a connection without ownership is subject to the thread-safety guarantees of the underlying method. Many of the methods on connection adapter classes are inherently multi-thread unsafe.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 436


def connections
  synchronize { @connections.dup }
end

#discard!

This method is for internal use only.

Discards all connections in the pool (even if they’re currently leased!), along with the pool itself. Any further interaction with the pool (except #spec and #schema_cache) is undefined.

See AbstractAdapter#discard!

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 478


def discard! # :nodoc:
  synchronize do
    return if self.discarded?
    @connections.each do |conn|
      conn.discard!
    end
    @connections = @available = @leases = nil
  end
end

#disconnect(raise_on_acquisition_timeout = true)

Disconnects all connections in the pool, and clears the pool.

Raises:

::ActiveRecord::ExclusiveConnectionTimeoutError if unable to gain ownership of all connections in the pool within a timeout interval (default duration is spec.db_config.checkout_timeout * 2 seconds).

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 446


def disconnect(raise_on_acquisition_timeout = true)
  with_exclusively_acquired_all_connections(raise_on_acquisition_timeout) do
    synchronize do
      @connections.each do |conn|
        if conn.in_use?
          conn.steal!
          checkin conn
        end
        conn.disconnect!
      end
      @connections = []
      @leases.clear
      @available.clear
    end
  end
end

#disconnect!

Disconnects all connections in the pool, and clears the pool.

The pool first tries to gain ownership of all connections. If unable to do so within a timeout interval (default duration is spec.db_config.checkout_timeout * 2 seconds), then the pool is forcefully disconnected without any regard for other connection owning threads.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 469


def disconnect!
  disconnect(false)
end

#flush(minimum_idle = @idle_timeout)

Disconnect all connections that have been idle for at least minimum_idle seconds. Connections currently checked out, or that were checked in less than minimum_idle seconds ago, are unaffected.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 637


def flush(minimum_idle = @idle_timeout)
  return if minimum_idle.nil?

  idle_connections = synchronize do
    return if self.discarded?
    @connections.select do |conn|
      !conn.in_use? && conn.seconds_idle >= minimum_idle
    end.each do |conn|
      conn.lease

      @available.delete conn
      @connections.delete conn
    end
  end

  idle_connections.each do |conn|
    conn.disconnect!
  end
end

#flush!

Disconnect all currently idle connections. Connections currently checked out are unaffected.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 659


def flush!
  reap
  flush(-1)
end

#inspect

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 272


def inspect # :nodoc:
  name_field = " name=#{db_config.name.inspect}" unless db_config.name == "primary"
  shard_field = " shard=#{@shard.inspect}" unless @shard == :default

  "#<#{self.class.name} env_name=#{db_config.env_name.inspect}#{name_field} role=#{role.inspect}#{shard_field}>"
end

#internal_metadata

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 300


def internal_metadata # :nodoc:
  InternalMetadata.new(self)
end

#lease_connection

Retrieve the connection associated with the current thread, or call #checkout to obtain one if necessary.

#lease_connection can be called any number of times; the connection is held in a cache keyed by a thread.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 309


def lease_connection
  lease = connection_lease
  lease.sticky = true
  lease.connection ||= checkout
end

#migration_context

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 288


def migration_context # :nodoc:
  MigrationContext.new(migrations_paths, schema_migration, internal_metadata)
end

#migrations_paths

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 292


def migrations_paths # :nodoc:
  db_config.migrations_paths || Migrator.migrations_paths
end

#new_connection (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 873


def new_connection
  connection = db_config.new_connection
  connection.pool = self
  connection
rescue ConnectionNotEstablished => ex
  raise ex.set_pool(self)
end

#num_waiting_in_queue

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 664


def num_waiting_in_queue # :nodoc:
  @available.num_waiting
end

#pin_connection!(lock_thread)

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 319


def pin_connection!(lock_thread) # :nodoc:
  @pinned_connection ||= (connection_lease&.connection || checkout)
  @pinned_connections_depth += 1

  # Any leased connection must be in @connections otherwise
  # some methods like #connected? won't behave correctly
  unless @connections.include?(@pinned_connection)
    @connections << @pinned_connection
  end

  @pinned_connection.lock_thread = ActiveSupport::IsolatedExecutionState.context if lock_thread
  @pinned_connection.verify! # eagerly validate the connection
  @pinned_connection.begin_transaction joinable: false, _lazy: false
end

#reap

Recover lost connections for the pool. A lost connection can occur if a programmer forgets to checkin a connection at the end of a thread or a thread dies unexpectedly.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 614


def reap
  stale_connections = synchronize do
    return if self.discarded?
    @connections.select do |conn|
      conn.in_use? && !conn.owner.alive?
    end.each do |conn|
      conn.steal!
    end
  end

  stale_connections.each do |conn|
    if conn.active?
      conn.reset!
      checkin conn
    else
      remove conn
    end
  end
end

#release(conn, owner_thread = conn.owner) (private)

Alias for #remove_connection_from_thread_cache.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 871


alias_method :release, :remove_connection_from_thread_cache

#release_connection(existing_lease = nil)

Signal that the thread is finished with the current connection. #release_connection releases the connection-thread association and returns the connection to the pool.

This method only works for connections that have been obtained through #lease_connection or #with_connection methods, connections obtained through #checkout will not be automatically released.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 382


def release_connection(existing_lease = nil)
  if conn = connection_lease.release
    checkin conn
    return true
  end
  false
end

#remove(conn)

Remove a connection from the connection pool. The connection will remain open and active but will no longer be managed by this pool.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 582


def remove(conn)
  needs_new_connection = false

  synchronize do
    remove_connection_from_thread_cache conn

    @connections.delete conn
    @available.delete conn

    # @available.any_waiting? => true means that prior to removing this
    # conn, the pool was at its max size (@connections.size == @size).
    # This would mean that any threads stuck waiting in the queue wouldn't
    # know they could checkout_new_connection, so let's do it for them.
    # Because condition-wait loop is encapsulated in the Queue class
    # (that in turn is oblivious to ConnectionPool implementation), threads
    # that are "stuck" there are helpless. They have no way of creating
    # new connections and are completely reliant on us feeding available
    # connections into the Queue.
    needs_new_connection = @available.any_waiting?
  end

  # This is intentionally done outside of the synchronized section as we
  # would like not to hold the main mutex while checking out new connections.
  # Thus there is some chance that needs_new_connection information is now
  # stale, we can live with that (bulk_make_new_connections will make
  # sure not to exceed the pool's @size limit).
  bulk_make_new_connections(1) if needs_new_connection
end

#remove_connection_from_thread_cache(conn, owner_thread = conn.owner) (private) Also known as: #release

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 868


def remove_connection_from_thread_cache(conn, owner_thread = conn.owner)
  @leases[owner_thread].clear(conn)
end

#schedule_query(future_result)

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 685


def schedule_query(future_result) # :nodoc:
  @async_executor.post { future_result.execute_or_skip }
  Thread.pass
end

#schema_cache

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 279


def schema_cache
  @schema_cache ||= BoundSchemaReflection.new(schema_reflection, self)
end

#schema_migration

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 296


def schema_migration # :nodoc:
  SchemaMigration.new(self)
end

#stat

Returns the connection pool’s usage statistic.

ActiveRecord::Base.connection_pool.stat # => { size: 15, connections: 1, busy: 1, dead: 0, idle: 0, waiting: 0, checkout_timeout: 5 }

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 671


def stat
  synchronize do
    {
      size: size,
      connections: @connections.size,
      busy: @connections.count { |c| c.in_use? && c.owner.alive? },
      dead: @connections.count { |c| c.in_use? && !c.owner.alive? },
      idle: @connections.count { |c| !c.in_use? },
      waiting: num_waiting_in_queue,
      checkout_timeout: checkout_timeout
    }
  end
end

#try_to_checkout_new_connection (private)

If the pool is not at a @size limit, establish new connection. Connecting to the DB is done outside main synchronized section.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 886


def try_to_checkout_new_connection
  # first in synchronized section check if establishing new conns is allowed
  # and increment @now_connecting, to prevent overstepping this pool's @size
  # constraint
  do_checkout = synchronize do
    if @threads_blocking_new_connections.zero? && (@connections.size + @now_connecting) < @size
      @now_connecting += 1
    end
  end
  if do_checkout
    begin
      # if successfully incremented @now_connecting establish new connection
      # outside of synchronized section
      conn = checkout_new_connection
    ensure
      synchronize do
        if conn
          adopt_connection(conn)
          # returned conn needs to be already leased
          conn.lease
        end
        @now_connecting -= 1
      end
    end
  end
end

#unpin_connection!

This method is for internal use only.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 334


def unpin_connection! # :nodoc:
  raise "There isn't a pinned connection #{object_id}" unless @pinned_connection

  clean = true
  @pinned_connection.lock.synchronize do
    @pinned_connections_depth -= 1
    connection = @pinned_connection
    @pinned_connection = nil if @pinned_connections_depth.zero?

    if connection.transaction_open?
      connection.rollback_transaction
    else
      # Something committed or rolled back the transaction
      clean = false
      connection.reset!
    end

    if @pinned_connection.nil?
      connection.steal!
      connection.lock_thread = nil
      checkin(connection)
    end
  end

  clean
end

#with_connection(prevent_permanent_checkout: false)

Yields a connection from the connection pool to the block. If no connection is already checked out by the current thread, a connection will be checked out from the pool, yielded to the block, and then returned to the pool when the block is finished. If a connection has already been checked out on the current thread, such as via #lease_connection or #with_connection, that existing connection will be the one yielded and it will not be returned to the pool automatically at the end of the block; it is expected that such an existing connection will be properly returned to the pool by the code that checked it out.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 399


def with_connection(prevent_permanent_checkout: false)
  lease = connection_lease
  sticky_was = lease.sticky
  lease.sticky = false if prevent_permanent_checkout

  if lease.connection
    begin
      yield lease.connection
    ensure
      lease.sticky = sticky_was if prevent_permanent_checkout && !sticky_was
    end
  else
    begin
      yield lease.connection = checkout
    ensure
      lease.sticky = sticky_was if prevent_permanent_checkout && !sticky_was
      release_connection(lease) unless lease.sticky
    end
  end
end

#with_exclusively_acquired_all_connections(raise_on_acquisition_timeout = true) (private)

Take control of all existing connections so a “group” action such as reload/disconnect can be performed safely. It is no longer enough to wrap it in synchronize because some pool’s actions are allowed to be performed outside of the main synchronize block.

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 727


def with_exclusively_acquired_all_connections(raise_on_acquisition_timeout = true)
  with_new_connections_blocked do
    attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout)
    yield
  end
end

#with_new_connections_blocked (private)

[ GitHub ]

# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 803


def with_new_connections_blocked
  synchronize do
    @threads_blocking_new_connections += 1
  end

  yield
ensure
  num_new_conns_required = 0

  synchronize do
    @threads_blocking_new_connections -= 1

    if @threads_blocking_new_connections.zero?
      @available.clear

      num_new_conns_required = num_waiting_in_queue

      @connections.each do |conn|
        next if conn.in_use?

        @available.add conn
        num_new_conns_required -= 1
      end
    end
  end

  bulk_make_new_connections(num_new_conns_required) if num_new_conns_required > 0
end

Class: ActiveRecord::ConnectionAdapters::ConnectionPool

Overview

Active Record Connection Pool

Introduction

Obtaining (checking out) a connection

Options

Class Method Summary

Instance Attribute Summary

Instance Method Summary

QueryCache::ConnectionPoolConfiguration - Included

Constructor Details

.new(pool_config) ⇒ ConnectionPool

Class Method Details

.install_executor_hooks(executor = ActiveSupport::Executor)

Instance Attribute Details

#active_connection (readonly)

#async_executor (readonly)

#automatic_reconnect (rw)

#checkout_timeout (rw)

#connected? ⇒ Boolean (readonly)

#db_config (readonly)

#discarded? ⇒ Boolean (readonly)

#permanent_lease? ⇒ Boolean (readonly)

#pool_config (readonly)

#reaper (readonly)

#role (readonly)

#schema_reflection (rw)

#schema_reflection=(schema_reflection) (rw)

#server_version (readonly)

#shard (readonly)

#size (readonly)

Instance Method Details

#acquire_connection(checkout_timeout) (private)

#active_connection? ⇒ Boolean (readonly) Also known as: #active_connection

#adopt_connection(conn) (private)

#attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout = true) (private)

#build_async_executor (private)

#bulk_make_new_connections(num_new_conns_needed) (private)

#checkin(conn)

#checkout(checkout_timeout = @checkout_timeout)

#checkout_and_verify(c) (private)

#checkout_for_exclusive_access(checkout_timeout) (private)

#checkout_new_connection (private)

#clear_reloadable_connections(raise_on_acquisition_timeout = true)

#clear_reloadable_connections!

#connection_class

#connection_lease (private)

#connections

#discard!

#disconnect(raise_on_acquisition_timeout = true)

#disconnect!

#flush(minimum_idle = @idle_timeout)

#flush!

#inspect

#internal_metadata

#lease_connection

#migration_context

#migrations_paths

#new_connection (private)

#num_waiting_in_queue

#pin_connection!(lock_thread)

#reap

#release(conn, owner_thread = conn.owner) (private)

#release_connection(existing_lease = nil)

#remove(conn)

#remove_connection_from_thread_cache(conn, owner_thread = conn.owner) (private) Also known as: #release

#schedule_query(future_result)

#schema_cache

#schema_migration

#stat

#try_to_checkout_new_connection (private)

#unpin_connection!

#with_connection(prevent_permanent_checkout: false)

#with_exclusively_acquired_all_connections(raise_on_acquisition_timeout = true) (private)

#with_new_connections_blocked (private)

`QueryCache::ConnectionPoolConfiguration` - Included

.new(pool_config) ⇒ `ConnectionPool`

#connected? ⇒ `Boolean` (readonly)

#discarded? ⇒ `Boolean` (readonly)

#permanent_lease? ⇒ `Boolean` (readonly)

#active_connection? ⇒ `Boolean` (readonly) Also known as: #active_connection