Safe Haskell	None
Language	Haskell2010

Hasql.Queue.Low.AtLeastOnce

Contents

Listing API
Advanced API

Description

A high throughput Session based API for a PostgreSQL backed queue.

Synopsis

enqueue :: Text -> Connection -> Value a -> [a] -> IO ()
withDequeue :: Text -> Connection -> Value a -> Int -> Int -> ([a] -> IO b) -> IO b
data PayloadId
failures :: Connection -> Value a -> Maybe PayloadId -> Int -> IO [(PayloadId, a)]
delete :: Connection -> [PayloadId] -> IO ()
withDequeueWith :: forall e a b. Exception e => WithNotifyHandlers -> Text -> Connection -> Value a -> Int -> Int -> ([a] -> IO b) -> IO b
data WithNotifyHandlers = WithNotifyHandlers {
- withNotifyHandlersAfterAction :: IO ()
- withNotifyHandlersBeforeNotification :: IO ()
}

Documentation

enqueue Source #

Arguments

:: Text	Notification channel name. Any valid PostgreSQL identifier
-> Connection	Connection
-> Value a	Payload encoder
-> [a]	List of payloads to enqueue
-> IO ()

Enqueue a list of payloads.

withDequeue Source #

Arguments

:: Text	Notification channel name. Any valid PostgreSQL identifier
-> Connection	Connection
-> Value a	Payload decoder
-> Int	Retry count
-> Int	Element count
-> ([a] -> IO b)	Continuation
-> IO b

Wait for the next payload and process it. If the continuation throws an exception the payloads are put back in the queue. IOError is caught and withDequeue will retry up to the retry count. If withDequeue fails after too many retries the final exception is rethrown. If individual payloads are are attempted more than the retry count they are set as "failed". See failures to receive the list of failed payloads.

If the queue is empty withDequeue will block until it recieves a notification from the PostgreSQL server.

Listing API

data PayloadId Source #

Internal payload id. Used by the public api as continuation token for pagination.

Instances

Eq PayloadId Source #
Instance details Defined in Hasql.Queue.Internal Methods (==) :: PayloadId -> PayloadId -> Bool # (/=) :: PayloadId -> PayloadId -> Bool #
Show PayloadId Source #
Instance details Defined in Hasql.Queue.Internal Methods showsPrec :: Int -> PayloadId -> ShowS # show :: PayloadId -> String # showList :: [PayloadId] -> ShowS #

failures Source #

Arguments

:: Connection
-> Value a	Payload decoder
-> Maybe PayloadId	Starting position of payloads. Pass `Nothing` to start at the beginning
-> Int	Count
-> IO [(PayloadId, a)]

Retrieve the payloads that have entered a failed state. See withDequeue for how that occurs. The function returns a list of values and an id. The id is used the starting place for the next batch of values. If Nothing is passed the list starts at the beginning.

delete :: Connection -> [PayloadId] -> IO () Source #

Permantently remove a failed payload.

Advanced API

withDequeueWith Source #

Arguments

:: Exception e
=> WithNotifyHandlers	Event handlers for events that occur as `withDequeWith` loops
-> Text	Notification channel name. Any valid PostgreSQL identifier
-> Connection	Connection
-> Value a	Payload decoder
-> Int	Retry count
-> Int	Element count
-> ([a] -> IO b)	Continuation
-> IO b

A more general configurable version of withDequeue. Unlike withDequeue one can specify the exception that causes a retry. Additionally event handlers can be specified to observe the internal behavior of the retry loop.

data WithNotifyHandlers Source #

To aid in observability and white box testing

Constructors

WithNotifyHandlers
Fields withNotifyHandlersAfterAction :: IO () An event that is trigger after the initial action, e.g. before dequeue is called. withNotifyHandlersBeforeNotification :: IO () An event that is triggered before the blocking on a notification.

Instances

Semigroup WithNotifyHandlers Source #
Instance details Defined in Hasql.Queue.Internal Methods (<>) :: WithNotifyHandlers -> WithNotifyHandlers -> WithNotifyHandlers # sconcat :: NonEmpty WithNotifyHandlers -> WithNotifyHandlers # stimes :: Integral b => b -> WithNotifyHandlers -> WithNotifyHandlers #
Monoid WithNotifyHandlers Source #
Instance details Defined in Hasql.Queue.Internal Methods mempty :: WithNotifyHandlers # mappend :: WithNotifyHandlers -> WithNotifyHandlers -> WithNotifyHandlers # mconcat :: [WithNotifyHandlers] -> WithNotifyHandlers #