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Boyang Chen updated KAFKA-9821: ------------------------------- Labels: need-kip (was: ) > Partition may skip assignment with static members and incremental rebalances > ---------------------------------------------------------------------------- > > Key: KAFKA-9821 > URL: https://issues.apache.org/jira/browse/KAFKA-9821 > Project: Kafka > Issue Type: Bug > Components: consumer, streams > Reporter: Guozhang Wang > Priority: Major > Labels: need-kip > > When static membership (KIP-345) and incremental rebalancing (KIP-429) are > turned on at the same time, that upon failure it is possible some partitions > are not assigned to anyone. The event sequence is the following: > 1. An assignment (task1) from rebalance is sent to an existing static member > with owned list (partition1, partition2), hence upon receiving the assignment > the static member is supposed to revoke partition2 and then re-join the group > to trigger another rebalance. > 2. The member crashed before re-join the group, lost all of its assigned > partitions. However since this member is static with long session timeout, it > was not kicked out of the group yet at the coordinator side. > 3. The member resumes and then re-join with a known instance.id. The > coordinator would not trigger a rebalance in this case and just give it the > previous assignment (partition1), and since the member has forgot about its > previous owned partitions it would just take partition1 and not re-join. > 4. As a result the partition2 is not owned by this member any more but not > re-assigned to anyone; until the next rebalance it would not be fetched by > any member of the group. > The key here is that today we are relying on the member's local memory to > calculate the added / revoked diff based on (owned, assigned). But if the > member crashed and lost all of its owned partition, AND if it is a static > member whose re-join would not trigger a new rebalance, this will break. > After thinking about that I think 1) on the consumer side, maybe we should > augment the Assignment protocol with an error code indicating > rebalance_needed which is going to be persisted on broker’s offset topic as > well so that consumer member can learn about this without comparing the > assignment with its owned partitions. > But 1) would affect the protocol and hence would only fix-forward future > versions; so 2) on the streams side, maybe we should leverage the existing > error field, to set REBALANCE_NEEDED for revocation as well (today it is only > set for version probing and a couple edge cases) so that streams can, upon > getting the error, force trigger a rebalance via the new consumer API. This > means that we can fix-backward in 2.4/2.5 as well. -- This message was sent by Atlassian Jira (v8.3.4#803005)