[GitHub] [kafka] splett2 commented on a diff in pull request #14053: KAFKA-15221; Fix the race between fetch requests from a rebooted follower.

[via GitHub]

splett2 commented on code in PR #14053:
URL: https://github.com/apache/kafka/pull/14053#discussion_r1322060958


##########
core/src/main/scala/kafka/cluster/Replica.scala:
##########
@@ -98,14 +103,21 @@ class Replica(val brokerId: Int, val topicPartition: 
TopicPartition) extends Log
    * fetch request is always smaller than the leader's LEO, which can happen 
if small produce requests are received at
    * high frequency.
    */
-  def updateFetchState(
+  def updateFetchStateOrThrow(
     followerFetchOffsetMetadata: LogOffsetMetadata,
     followerStartOffset: Long,
     followerFetchTimeMs: Long,
     leaderEndOffset: Long,
     brokerEpoch: Long
   ): Unit = {
     replicaState.updateAndGet { currentReplicaState =>
+      // Fence the update if it provides a stale broker epoch.
+      val expectedBrokerEpoch = currentReplicaState.brokerEpoch.getOrElse(-1L)
+      if (brokerEpoch != -1 && brokerEpoch < expectedBrokerEpoch) {
+        throw Errors.NOT_LEADER_OR_FOLLOWER.exception(s"Received stale fetch 
state update. broker epoch=$brokerEpoch " +
+          s"vs expected=$expectedBrokerEpoch")
+      }

Review Comment:
   we can probably simplify this to something like:
   `if (currentReplicaState.brokerEpoch.exists(_ > brokerEpoch))`
   
   I think we can also directly just throw `NotLeaderOrFollowerException` 
instead of redirecting through `Errors.NOT_LEADER_OR_FOLLOWER.exception`.



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