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Jason Gustafson resolved KAFKA-8635. ------------------------------------ Resolution: Fixed Fix Version/s: 2.3.1 2.4.0 > Unnecessary wait when looking up coordinator before transactional request > ------------------------------------------------------------------------- > > Key: KAFKA-8635 > URL: https://issues.apache.org/jira/browse/KAFKA-8635 > Project: Kafka > Issue Type: Bug > Components: clients > Affects Versions: 2.3.0, 2.2.1 > Reporter: Denis Washington > Assignee: Bob Barrett > Priority: Major > Fix For: 2.4.0, 2.3.1 > > > In our Kafka Streams applications (with EOS enabled), we were seeing > mysterious long delays between records being produced by a stream task and > the same records being consumed by the next task. These delays turned out to > always be around {{retry.backoff.ms}} long; reducing that value reduced the > delays by about the same amount. > After digging further, I pinned down the problem to the following lines in > {{org.apache.kafka.clients.producer.internals.Sender#runOnce}}: > {{} else if (transactionManager.hasInFlightTransactionalRequest() || > maybeSendTransactionalRequest()) {}} > {{ // as long as there are outstanding transactional requests, we simply > wait for them to return}}}} > {{ client.poll(retryBackoffMs, time.milliseconds());}}}}}} > {{ return;}} > {{}}} > This code seems to assume that, if {{maybeSendTransactionalRequest}} returns > true, a transactional request has been sent out that should be waited for. > However, this is not true if the request requires a coordinator lookup: > {{if (nextRequestHandler.needsCoordinator()) {}} > {{ targetNode = > transactionManager.coordinator(nextRequestHandler.coordinatorType());}} > {{ if (targetNode == null) {}} > {{ transactionManager.lookupCoordinator(nextRequestHandler); }}}}}} > {{ break;}} > {{ }}} > {{ ...}} > {{lookupCoordinator()}} does not actually send anything, but just enqueues a > coordinator lookup request for the {{Sender}}'s next run loop iteration. > {{maybeSendTransactionalRequest}} still returns true, though (the {{break}} > jumps to a {{return true}} at the end of the method), leading the {{Sender}} > to needlessly wait via {{client.poll()}} although there is actually no > request in-flight. > I _think_ the fix is to let {{maybeSendTransactionalRequest}} return false if > it merely enqueues the coordinator lookup instead of actually sending > anything. But I'm not sure, hence the bug report instead of a pull request. -- This message was sent by Atlassian JIRA (v7.6.14#76016)