[KAFKA-8400] Do not update follower replica state if the log read failed

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.4.0
• Assignee: Jason Gustafson
• Reporter: Jason Gustafson
• Created: 21/May/19 02:12
• Updated: 05/Jun/19 21:37
• Resolved: 05/Jun/19 21:37

Description

In ReplicaManager.fetchMessages, we have the following logic to read from the log and update follower state:

    val result = readFromLocalLog(
        replicaId = replicaId,
        fetchOnlyFromLeader = fetchOnlyFromLeader,
        fetchIsolation = fetchIsolation,
        fetchMaxBytes = fetchMaxBytes,
        hardMaxBytesLimit = hardMaxBytesLimit,
        readPartitionInfo = fetchInfos,
        quota = quota)
      if (isFromFollower) updateFollowerLogReadResults(replicaId, result)
      else result

The call to readFromLocalLog could fail for many reasons, in which case we return a LogReadResult with an error set and all fields set to -1. The problem is that we do not check for the error when updating the follower state. As far as I can tell, this does not cause any correctness issues, but we're just asking for trouble. It would be better to check the error before proceeding to `Partition.updateReplicaLogReadResult`.

Perhaps even better would be to have readFromLocalLog return something like Either[LogReadResult, Errors] so that we are forced to handle the error.

Issue Links

• links to: GitHub Pull Request #6814