Updatable consumer settings

[scottf]

According to unit tests in the Java client, you can update these settings in a consumer:

• deliverSubject
• ackWait
• rateLimit
• maxAckPending
• maxDeliver

and these settings you cannot update:

• deliverPolicy
• filterSubject
• idleHeartbeat

Code Reference:

• Server Implementation

Java unit tests:

• testValidConsumerUpdates
• testInvalidConsumerUpdates

In practice, this only applies to a durable consumer, but if you know the internal name of an ephemeral consumer, you might be able to update it's settings. This has not been verified.

[tbeets]

I assume filterSubject cannot be changed because doing so would change all prior sequencing and working set assumptions (i.e. fundamentally changing the view of the underlying stream). Is that correct?

[ripienaar]

https://github.com/nats-io/nats-server/blob/297b44394f92e990da450178cffaa7adecc88837/server/consumer.go#L1216