c96a43d · typeable/postgresql-simple

git.iko.soy/typeable/postgresql-simple

Change withTransactionModeRetry to allow the user to determine when to retry

withTransactionModeRetry previously would retry if a not_serializable exception was thrown, but this can be a little too fine grained. There are cases when a transaction should be retried when a unique_violation occurs (e.g., a race condition occurs). This allows users to tune the retrying semantics to the needs of their application.

commitc96a43d4fdffc59ef355c81f597e24a44f76478e authorOliver Charles <oliver.g.charles@googlemail.com> dateSun 14 Oct 2012, 12:41 (14 years ago) parent9ac2ee0

1 file changed+19−13

compare with master

unifiedsplit

src/Database/PostgreSQL/Simple.hs+19−13

src/Database/PostgreSQL/Simple.hs+19−13

@@ -663,6 +663,15 @@ withTransactionSerializable =

663663 { isolationLevel = Serializable

664664 , readWriteMode = ReadWrite

665665 }

666+ retryOnNotSerializable

667+ where

668+ retryOnNotSerializable exception =

669+ case exception of

670+ SqlError{..} | sqlState == serialization_failure

671+ -> True

672+ _ -> False

673+ -- http://www.postgresql.org/docs/current/static/errcodes-appendix.html

674+ serialization_failure = "40001"

666675

667676-- | Execute an action inside a SQL transaction with a given isolation level.

668677withTransactionLevel :: IsolationLevel -> Connection -> IO a -> IO a

@@ -678,14 +687,15 @@ withTransactionMode mode conn act =

678687 commit conn

679688 return r

680689

681−-- | Like 'withTransactionMode', but if a 'SqlError' arises whose 'sqlState' is

682−-- @\"40001\"@ (@serialization_failure@), this will issue a @ROLLBACK@, then

683−-- try the action again. If any other exception arises, this will issue a

684−-- @ROLLBACK@, but will propagate the exception instead of retrying.

690+-- | Like 'withTransactionMode', but also takes a custom callback to

691+-- determine if a transaction should be retried if an 'SqlError' occurs.

692+-- If the callback returns True, then the transaction will be retried.

693+-- If the callback returns False, or an exception other than an 'SqlError'

694+-- occurs then the transaction will be rolled back and the exception rethrown.

685695--

686696-- This is used to implement 'withTransactionSerializable'.

687−withTransactionModeRetry :: TransactionMode -> Connection -> IO a -> IO a

688−withTransactionModeRetry mode conn act =

697+withTransactionModeRetry :: TransactionMode -> (SqlError -> Bool) -> Connection -> IO a -> IO a

698+withTransactionModeRetry mode shouldRetry conn act =

689699 mask $ \restore ->

690700 retryLoop $ try $ do

691701 a <- restore act

@@ -699,16 +709,12 @@ withTransactionModeRetry mode conn act =

699709 case r of

700710 Left e -> do

701711 rollback conn

702− case fromException e of

703− Just SqlError{..} | sqlState == serialization_failure

704− -> retryLoop act'

705− _ -> throwIO e

712+ case fmap shouldRetry (fromException e) of

713+ Just True -> retryLoop act'

714+ _ -> throwIO e

706715 Right a ->

707716 return a

708717

709− -- http://www.postgresql.org/docs/current/static/errcodes-appendix.html

710− serialization_failure = "40001"

711−

712718-- | Rollback a transaction.

713719rollback :: Connection -> IO ()

714720rollback conn = execute_ conn "ABORT" >> return ()