[GitHub] [kafka] junrao commented on a change in pull request #9631: KAFKA-9672: Leader with ISR as a superset of replicas

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junrao commented on a change in pull request #9631:
URL: https://github.com/apache/kafka/pull/9631#discussion_r529070546



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File path: core/src/main/scala/kafka/cluster/Partition.scala
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@@ -947,9 +947,10 @@ class Partition(val topicPartition: TopicPartition,
                                   leaderEndOffset: Long,
                                   currentTimeMs: Long,
                                   maxLagMs: Long): Boolean = {
-    val followerReplica = getReplicaOrException(replicaId)
-    followerReplica.logEndOffset != leaderEndOffset &&
-      (currentTimeMs - followerReplica.lastCaughtUpTimeMs) > maxLagMs
+    getReplica(replicaId).fold(true) { followerReplica =>

Review comment:
       For the reassignment case, once the controller shrinks the assigned replica set, the next step is for the controller to remove the remove replica from ISR and bump up the leader epoch. The shrunk isr will then be propagated to the leader. With `fold(true)`, we allow to leader to shrink ISR immediately. This might be ok, but is unnecessary work since the controller will be doing that soon.
   
   Another option is to use `fold(false)`. This way, the leader won't shrink the removed replica from ISR. Only the controller will do.
   




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