KAFKA-19354: KRaft observer should fetch from leader after rediscovery #19854
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ahuang98
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May 30, 2025
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| context.pollUntilRequest(); | ||
| fetchRequest = context.assertSentFetchRequest(); | ||
| assertEquals(leaderId, fetchRequest.destination().id()); |
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this check would fail without the fix
ahuang98
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jsancio
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Jun 2, 2025
raft/src/test/java/org/apache/kafka/raft/KafkaRaftClientTest.java
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raft/src/test/java/org/apache/kafka/raft/KafkaRaftClientTest.java
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raft/src/test/java/org/apache/kafka/raft/KafkaRaftClientTest.java
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raft/src/test/java/org/apache/kafka/raft/KafkaRaftClientTest.java
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raft/src/test/java/org/apache/kafka/raft/KafkaRaftClientTest.java
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Thanks for the review Jose
Yes, this doesn't impact voters because prospectives which have a leaderId would transition back to follower (and refreshed fetch timeout) |
ahuang98
commented
Jun 9, 2025
| } else if (leaderId.isPresent()) { | ||
| if (quorum.isFollowerObserver()) { | ||
| // This allows observers to resume fetching from leader after discovering the leader | ||
| // transitionToFollower(epoch, leaderId.getAsInt(), leaderEndpoints, currentTimeMs); |
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alternative solution, needing allowance for follower to follower transition for observers only
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Observers may get stuck fetching from bootstrap servers even on discovery of a leader from a fetch response.
This allows observers to start fetching from the leader again by reseting their fetch timeout on discovery of a leader from a fetch response. (Observers fetch from bootstrap servers once their fetch timeout expires)
testObserverSendDiscoveryFetchAfterFetchTimeoutAndResumesFetchingFromLeaderdemonstrates the issue that observers will get stuck fetching from random bootstrap servers after fetch timeout (fails without the change)
testUnattachedWithLeaderCanBecomeFollowerAfterFindingLeadershowsvoters are not susceptible to getting stuck fetching from bootstrap servers