divijvaidya commented on code in PR #12590:
URL: https://github.com/apache/kafka/pull/12590#discussion_r968407998


##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/Fetcher.java:
##########
@@ -1933,11 +1941,76 @@ private Map<String, String> 
topicPartitionTags(TopicPartition tp) {
         }
     }
 
+    // Visible for testing
+    void maybeCloseFetchSessions(final Timer timer) {
+        final Cluster cluster = metadata.fetch();
+        final List<RequestFuture<ClientResponse>> requestFutures = new 
ArrayList<>();
+        for (final Map.Entry<Integer, FetchSessionHandler> entry : 
sessionHandlers.entrySet()) {
+            final FetchSessionHandler sessionHandler = entry.getValue();
+            // set the session handler to notify close. This will set the next 
metadata request to send close message.
+            sessionHandler.notifyClose();
+            final Integer fetchTargetNodeId = entry.getKey();
+
+            // Fet
+            final Node fetchTarget = cluster.nodeById(fetchTargetNodeId);
+            if (fetchTarget == null || client.isUnavailable(fetchTarget)) {
+                log.debug("Skip sending close session request to broker {} 
since it is not reachable", fetchTarget);
+                continue;
+            }
+            final RequestFuture<ClientResponse> responseFuture = 
sendFetchRequestToNode(sessionHandler.newBuilder().build(), fetchTarget);
+            responseFuture.addListener(new 
RequestFutureListener<ClientResponse>() {
+                @Override
+                public void onSuccess(ClientResponse value) {
+                    log.info("Successfully sent a close message to {} for 
session {}", fetchTargetNodeId, sessionHandler.sessionId());
+                }
+
+                @Override
+                public void onFailure(RuntimeException e) {
+                    log.warn("Unable to send a close message to {} for session 
{}. " +
+                        "This may result in unnecessary fetch sessions at the 
broker.", fetchTargetNodeId, sessionHandler.sessionId(), e);

Review Comment:
   This scenario (when sending a close request to the server fails) should not 
ideally occur. It is an error condition but we want to ignore the error since 
the system can recover (the session would be removed on the server when it 
times out) from it. In such cases of recoverable error, I prefer to add a warn 
so that the user can identify it as something unexpected that occurred on the 
system. The action that the user could take will be based on the exception 
trace printed here (perhaps their auth creds were incorrect?).
   
   For the other case of log.warn a few lines below this, in the upcoming 
commit, I have added a suggestion to the user to increase the close timeout for 
KafkaConsumer. 



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