[GitHub] [kafka] rajinisivaram commented on a change in pull request #9382: KAFKA-10554; Perform follower truncation based on diverging epochs in Fetch response

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rajinisivaram commented on a change in pull request #9382:
URL: https://github.com/apache/kafka/pull/9382#discussion_r501199512



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File path: core/src/main/scala/kafka/server/AbstractFetcherThread.scala
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@@ -432,14 +455,22 @@ abstract class AbstractFetcherThread(name: String,
       failedPartitions.removeAll(initialFetchStates.keySet)
 
       initialFetchStates.forKeyValue { (tp, initialFetchState) =>
-        // We can skip the truncation step iff the leader epoch matches the existing epoch
+        // For IBP 2.7 onwards, we can rely on truncation based on diverging data returned in fetch responses.
+        // For older versions, we can skip the truncation step iff the leader epoch matches the existing epoch
         val currentState = partitionStates.stateValue(tp)
-        val updatedState = if (currentState != null && currentState.currentLeaderEpoch == initialFetchState.leaderEpoch) {
+        val updatedState = if (initialFetchState.offset >= 0 && isTruncationOnFetchSupported && initialFetchState.lastFetchedEpoch.nonEmpty) {

Review comment:
       @rite2nikhil Thanks for the review. Did you mean changing this to:
   ```
   if (isTruncationOnFetchSupported && initialFetchState.lastFetchedEpoch.nonEmpty && initialFetchState.offset >= 0)
   ```




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