Fix: JetStream ackWait timer starts before handler due to pre-buffering (#609)#37
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Abzaek wants to merge 1 commit into
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Fix: JetStream ackWait timer starts before handler due to pre-buffering (#609)#37Abzaek wants to merge 1 commit into
Abzaek wants to merge 1 commit into
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consumer.Consume() internally pre-fetches messages, causing NATS' ackWait clock to start ticking before the handler callback fires. With slow handlers or large backlogs, NATS redelivers messages that are still being processed, causing duplicate processing. Fix by adding PullMaxMessages(1) to consume options, which tells NATS to deliver one message at a time, keeping the ackWait clock aligned with actual handler execution time. Fixes #609
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Summary
Fixes a timing bug in
consumer.Consume()where NATS JetStream internal pre-buffering causes the ackWait clock to start ticking before the handler callback fires.Root Cause
consumer.Consume()pre-fetches messages into an internal buffer. NATS JetStream starts the ackWait clock when messages are delivered to the consumer, but watermill only starts its ackWait timer whenhandleMsgis called. With slow handlers or large backlogs, the real elapsed time far exceedsAckWaitTimeout, causing NATS to redeliver messages that are still being processed — resulting in duplicate processing.Fix
Added
jetstream.PullMaxMessages(1)to consume options. This limits NATS to deliver one message at a time, keeping the ackWait clock aligned with actual handler execution time.Before/After
Before:
consumer.Consume(cb)— pre-fetches N messages, ackWait for each starts when pulled by NATSAfter:
consumer.Consume(cb, PullMaxMessages(1))— delivers one at a time, ackWait aligns with handlerFixes #609