Database.PostgreSQL.Simple.Notification

Support for receiving asynchronous notifications via PostgreSQL's Listen/Notify mechanism. See https://www.postgresql.org/docs/9.5/static/sql-notify.html for more information.

Note that on Windows, getNotification currently uses a polling loop of 1 second to check for more notifications, due to some inadequacies in GHC's IO implementation and interface on that platform. See GHC issue #7353 for more information. While this workaround is less than ideal, notifications are still better than polling the database directly. Notifications do not create any extra work for the backend, and are likely cheaper on the client side as well.

https://hackage.haskell.org/trac/ghc/ticket/7353

Documentation

data Notification

Constructors

Notification

Fields

• notificationPid :: !CPid
• notificationChannel :: !ByteString
• notificationData :: !ByteString

Instances

Eq Notification

Defined in Database.PostgreSQL.Simple.Notification

Methods

(==) :: Notification -> Notification -> Bool

(/=) :: Notification -> Notification -> Bool

Show Notification

Defined in Database.PostgreSQL.Simple.Notification

Methods

showsPrec :: Int -> Notification -> ShowS

show :: Notification -> String

showList :: [Notification] -> ShowS

getNotification :: Connection -> IO Notification

Returns a single notification. If no notifications are available, getNotification blocks until one arrives.

It is safe to call getNotification on a connection that is concurrently being used for other purposes, note however that PostgreSQL does not deliver notifications while a connection is inside a transaction.

getNotificationNonBlocking :: Connection -> IO (Maybe Notification)

Non-blocking variant of getNotification. Returns a single notification, if available. If no notifications are available, returns Nothing.

getBackendPID :: Connection -> IO CPid

Returns the process CPid of the backend server process handling this connection.

The backend PID is useful for debugging purposes and for comparison to NOTIFY messages (which include the PID of the notifying backend process). Note that the PID belongs to a process executing on the database server host, not the local host!