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Boyang Chen commented on KAFKA-7610: ------------------------------------ Sounds good Jason! I think combining `group.max.size` and member id requirement in join group request should be sufficient for the solving the above scenario. I will open a separate Jira for group size, in the meanwhile I think the conclusion is that Jason's original proposal 2 should be sufficient to mitigate the problem. > Detect consumer failures in initial JoinGroup > --------------------------------------------- > > Key: KAFKA-7610 > URL: https://issues.apache.org/jira/browse/KAFKA-7610 > Project: Kafka > Issue Type: Improvement > Reporter: Jason Gustafson > Priority: Major > > The session timeout and heartbeating logic in the consumer allow us to detect > failures after a consumer joins the group. However, we have no mechanism to > detect failures during a consumer's initial JoinGroup when its memberId is > empty. When a client fails (e.g. due to a disconnect), the newly created > MemberMetadata will be left in the group metadata cache. Typically when this > happens, the client simply retries the JoinGroup. Every retry results in a > new dangling member created and left in the group. These members are doomed > to a session timeout when the group finally finishes the rebalance, but > before that time, they are occupying memory. In extreme cases, when a > rebalance is delayed (possibly due to a buggy application), this cycle can > repeat and the cache can grow quite large. > There are a couple options that come to mind to fix the problem: > 1. During the initial JoinGroup, we can detect failed members when the TCP > connection fails. This is difficult at the moment because we do not have a > mechanism to propagate disconnects from the network layer. A potential option > is to treat the disconnect as just another type of request and pass it to the > handlers through the request queue. > 2. Rather than holding the JoinGroup in purgatory for an indefinite amount of > time, we can return earlier with the generated memberId and an error code > (say REBALANCE_IN_PROGRESS) to indicate that retry is needed to complete the > rebalance. The consumer can then poll for the rebalance using its assigned > memberId. And we can detect failures through the session timeout. Obviously > this option requires a KIP (and some more thought). -- This message was sent by Atlassian JIRA (v7.6.3#76005)