[jira] [Created] (KAFKA-20449) OffsetFetcherUtils.updateSubscriptionState logs at WARN for benign race condition during rebalance

["Tamas Kornai (Jira)" <ji...@apache.org>]

Tamas Kornai created KAFKA-20449:
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             Summary: OffsetFetcherUtils.updateSubscriptionState logs at WARN for benign race condition during rebalance
                 Key: KAFKA-20449
                 URL: https://issues.apache.org/jira/browse/KAFKA-20449
             Project: Kafka
          Issue Type: Bug
          Components: clients, consumer
    Affects Versions: 4.1.2, 4.3.0, 4.2.1
            Reporter: Tamas Kornai


KAFKA-20131 introduced a log.warn() in OffsetFetcherUtils.updateSubscriptionState() for the case where a LIST_OFFSETS response arrives after the partition has already been revoked:

{code:java}
log.warn("Not updating high watermark for partition {} as it is no longer assigned", partition);
{code}

This is a benign race condition that naturally occurs during consumer group rebalances — a LIST_OFFSETS request is issued, the partition gets revoked before the response returns, and the response is simply
discarded. No data loss or correctness issue arises.

However, the WARN level is problematic in practice. Many organizations use warning log rates as a signal for canary release health. Since rebalances are frequent during rolling deployments, canary instances
generate a high volume of these warnings, which triggers automated rollback of otherwise healthy releases.

The log should be downgraded to DEBUG (or at most INFO), since it describes expected, harmless behavior that requires no operator action.

Affected code:

clients/src/main/java/org/apache/kafka/clients/consumer/internals/OffsetFetcherUtils.java, lines 281-285 (introduced in commit abcbef6a4c, PR #21457).

Both log statements are affected:
- "Not updating high watermark for partition {} as it is no longer assigned" (READ_UNCOMMITTED)
- "Not updating last stable offset for partition {} as it is no longer assigned" (READ_COMMITTED)



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