Silence WARNs during rebalancing

[mauhiz]

On decaton 6, observing the following WARNs, when

• cooperating rebalancing is ON
• a node joins the consumer group

com.linecorp.decaton.processor.runtime.internal.CommitManager:131

Offset commit failed asynchronously

org.apache.kafka.common.errors.RebalanceInProgressException: Offset commit cannot be completed since the consumer is undergoing a rebalance for auto partition assignment. You can try completing the rebalance by calling poll() and then retry the operation.

I don't think the end-user needs to know about this, since poll() is soon going to be called again in ProcessorSubscription.consumeLoop

[ocadaruma]

Thanks for reporting the issue.

However, I prefer to keep WARN level for these commit failures because:

• Though Decaton doesn't assume commit-failure is fatal as commit is attempted soon as you pointed out, still it's a sign of duplicate processing (this is also normal in Decaton (Kafka) though), which some users may care about.
• I hope RebalanceInProgressException due to cooperative rebalancing will be solved in upstream in the future
  • https://issues.apache.org/jira/browse/KAFKA-9382

So I would like to keep WARN by default for these commit-failure. Users still can silence if necessary by logger config (e.g. logback).

[mauhiz]

Can you recommend a way to only silence retryable commit exceptions?
As far as I know logback config doesn't allow to filter log level by keyword in the stacktrace

[ocadaruma]

I think you can try EvaluationFilter and set the expression like

<expression>return throwable instanceof org.apache.kafka.clients.consumer.RetriableCommitFailedException;</expression>

[mauhiz]

okay, I don't know if it has reasonable performance, but at least there is a way :-)