Integration / Apache Pulsar Interview questions

What happens when a consumer negatively acknowledges a message?

A negative acknowledgment (nack) tells the broker that this specific consumer failed to process the message and it should be redelivered - typically after a configurable redelivery delay - rather than being treated as successfully handled.

Unlike an acknowledgment timeout (which waits for a consumer to go silent for a period before assuming failure), a nack is an explicit, immediate signal from the consumer's own processing logic that something went wrong with that particular message.

Depending on the subscription type, the redelivered message may go to the same consumer or a different one, and if it keeps failing repeatedly, a configured dead letter policy can route it to a separate dead letter topic instead of endlessly retrying.

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A nack signals to the broker that: the topic should be compacted

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the subscription should be deleted

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this message should be redelivered because processing failed

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Messages that repeatedly fail can be routed to a: dead letter topic, if configured

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the schema registry

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tiered storage automatically

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