nats-io / gnatsd / 1667

91%

Pull #571

travis-ci

Implement DLQ

With gnatsd, there is no way of knowing if a message was delivered (or
attempted to be delivered) to a subscriber. However, the server knows
this information when it receives a published message. If there are no
subscribers, the message is dropped on the floor. Typically,
error-handling/timeout/retry logic should be handled by the client, but
in the case where there is no interest on the subject, it's moot.

There are a number of concrete use cases outside of administrative/
monitoring functions where this is useful, including NATS Streaming.
See #568 for further motivation behind this.

As implemented, DLQs are off by default, so there is no performance
impact. In practice, the only performance impact is when messages
are dropped, which seems like a vanity metric anyway.

Resolves #568 and #352.

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