This module utilizes PostgreSQL to implement a durable queue for efficently processing payloads.
Typically a producer would enqueue a new payload as part of larger database transaction
createAccount userRecord = transaction Serializable Write $ do
createUser userRecord
enqueue "queue_channel" emailEncoder [makeVerificationEmail userRecord]In another thread or process the consumer would drain the queue.
-- Wait for a single new record and try to send the email 5 times for giving
-- up and marking the payload as failed.
forever $ withDequeue "queue_channel" conn emailDecoder 5 1 $
mapM_ sendEmail