Re: [PR] KAFKA-19950: Mark session stale when removed prior disconnection event [kafka]

["adixitconfluent (via GitHub)" <gi...@apache.org>]

adixitconfluent commented on code in PR #21062:
URL: https://github.com/apache/kafka/pull/21062#discussion_r2584990456


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server/src/main/java/org/apache/kafka/server/share/session/ShareSessionCache.java:
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@@ -172,6 +169,17 @@ public synchronized ShareSession remove(ShareSession session) {
         if (removeResult != null) {
             numPartitions = numPartitions - session.cachedSize();
             numMembersPerGroup.compute(session.key().groupId(), (k, v) -> v != null ? v - 1 : 0);
+            // Mark the session as stale in the connectionIdToSessionMap to avoid removing
+            // the active session for the client. When client re-sends the initial epoch where the
+            // broker removes the prior session and establishes new session, then sometimes the connection
+            // id is changed. This leads to removal of the new session from the cache, when old connection
+            // disconnect event is processed. Marking the old connection as stale avoids this issue.
+            // If the connection id remains same for both old and new session, then the subsequent call
+            // for session creation will overwrite the prior stale mapping in the connectionIdToSessionMap.

Review Comment:
   this comment is confusing to me. If the connection id remains same for both old and new session, it will be the same session, not different.



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