Class: ActiveRecord::ConnectionAdapters::ConnectionPool

Inherits:
Object
  • Object
show all
Includes:
AbstractPool, QueryCache::ConnectionPoolConfiguration, MonitorMixin
Defined in:
lib/active_record/connection_adapters/abstract/connection_pool.rb,
lib/active_record/connection_adapters/abstract/connection_pool/queue.rb,
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:

  1. 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.

  2. 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).

  3. 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).

– Synchronization policy:

  • all public methods can be called outside synchronize

  • access to these instance variables needs to be in synchronize:

    • @connections

    • @now_connecting

  • private methods that require being called in a synchronize blocks are now explicitly documented

Defined Under Namespace

Modules: BiasableQueue, ExecutorHooks Classes: ConnectionLeasingQueue, Lease, LeaseRegistry, Queue, Reaper, WeakThreadKeyMap

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from QueryCache::ConnectionPoolConfiguration

#clear_query_cache, #dirties_query_cache, #disable_query_cache, #disable_query_cache!, #enable_query_cache, #enable_query_cache!, #query_cache, #query_cache_enabled

Constructor Details

#initialize(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.



227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 227

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

Instance Attribute Details

#async_executor ⇒ Object (readonly)

Returns the value of attribute async_executor.



217
218
219
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 217

def async_executor
  @async_executor
end

#automatic_reconnect ⇒ Object

Returns the value of attribute automatic_reconnect.



216
217
218
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216

def automatic_reconnect
  @automatic_reconnect
end

#checkout_timeout ⇒ Object

Returns the value of attribute checkout_timeout.



216
217
218
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 216

def checkout_timeout
  @checkout_timeout
end

#db_config ⇒ Object (readonly)

Returns the value of attribute db_config.



217
218
219
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 217

def db_config
  @db_config
end

#pool_config ⇒ Object (readonly)

Returns the value of attribute pool_config.



217
218
219
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 217

def pool_config
  @pool_config
end

#reaper ⇒ Object (readonly)

Returns the value of attribute reaper.



217
218
219
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 217

def reaper
  @reaper
end

#role ⇒ Object (readonly)

Returns the value of attribute role.



217
218
219
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 217

def role
  @role
end

#shard ⇒ Object (readonly)

Returns the value of attribute shard.



217
218
219
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 217

def shard
  @shard
end

#size ⇒ Object (readonly)

Returns the value of attribute size.



217
218
219
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 217

def size
  @size
end

Class Method Details

.install_executor_hooks(executor = ActiveSupport::Executor) ⇒ Object 



207
208
209
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 207

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

Instance Method Details

#active_connection? ⇒ Boolean 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?

Returns:

  • (Boolean) 


379
380
381
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 379

def active_connection?
  connection_lease.connection
end

#checkin(conn) ⇒ Object

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.



573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 573

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) ⇒ Object

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.



550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 550

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

#clear_reloadable_connections(raise_on_acquisition_timeout = true) ⇒ Object

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).



508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 508

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! ⇒ Object

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.



532
533
534
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 532

def clear_reloadable_connections!
  clear_reloadable_connections(false)
end

#connected? ⇒ Boolean

Returns true if a connection has already been opened.

Returns:

  • (Boolean) 


430
431
432
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 430

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

#connection ⇒ Object 



320
321
322
323
324
325
326
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 320

def connection
  ActiveRecord.deprecator.warn(<<~MSG)
    ActiveRecord::ConnectionAdapters::ConnectionPool#connection is deprecated
    and will be removed in Rails 8.0. Use #lease_connection instead.
  MSG
  lease_connection
end

#connection_class ⇒ Object

:nodoc:



370
371
372
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 370

def connection_class # :nodoc:
  pool_config.connection_class
end

#connections ⇒ Object

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.



445
446
447
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 445

def connections
  synchronize { @connections.dup }
end

#discard! ⇒ Object

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!



487
488
489
490
491
492
493
494
495
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 487

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

#discarded? ⇒ Boolean

:nodoc:

Returns:

  • (Boolean) 


497
498
499
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 497

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

#disconnect(raise_on_acquisition_timeout = true) ⇒ Object

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).



455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 455

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! ⇒ Object

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.



478
479
480
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 478

def disconnect!
  disconnect(false)
end

#flush(minimum_idle = @idle_timeout) ⇒ Object

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.



646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 646

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! ⇒ Object

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



668
669
670
671
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 668

def flush!
  reap
  flush(-1)
end

#inspect ⇒ Object

:nodoc:



273
274
275
276
277
278
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 273

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 ⇒ Object

:nodoc:



301
302
303
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 301

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

#lease_connection ⇒ Object

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.



310
311
312
313
314
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 310

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

#migration_context ⇒ Object

:nodoc:



289
290
291
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 289

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

#migrations_paths ⇒ Object

:nodoc:



293
294
295
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 293

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

#num_waiting_in_queue ⇒ Object

:nodoc:



673
674
675
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 673

def num_waiting_in_queue # :nodoc:
  @available.num_waiting
end

#permanent_lease? ⇒ Boolean

:nodoc:

Returns:

  • (Boolean) 


316
317
318
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 316

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

#pin_connection!(lock_thread) ⇒ Object

:nodoc:



328
329
330
331
332
333
334
335
336
337
338
339
340
341
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 328

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 ⇒ Object

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.



623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 623

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_connection(existing_lease = nil) ⇒ Object

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.



391
392
393
394
395
396
397
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 391

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

#remove(conn) ⇒ Object

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



591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 591

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

#schedule_query(future_result) ⇒ Object

:nodoc:



694
695
696
697
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 694

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

#schema_cache ⇒ Object 



280
281
282
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 280

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

#schema_migration ⇒ Object

:nodoc:



297
298
299
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 297

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

#schema_reflection=(schema_reflection) ⇒ Object 



284
285
286
287
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 284

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

#stat ⇒ Object

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 }



680
681
682
683
684
685
686
687
688
689
690
691
692
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 680

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

#unpin_connection! ⇒ Object

:nodoc:



343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 343

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) ⇒ Object

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.



408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
 
# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 408

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