[GitHub] [kafka] guozhangwang commented on a change in pull request #11057: KAFKA-13008: Try to refresh end offset when partitionLag returns empty

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guozhangwang commented on a change in pull request #11057:
URL: https://github.com/apache/kafka/pull/11057#discussion_r675158219



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File path: clients/src/main/java/org/apache/kafka/clients/consumer/KafkaConsumer.java
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@@ -2237,7 +2237,21 @@ public OptionalLong currentLag(TopicPartition topicPartition) {
         acquireAndEnsureOpen();
         try {
             final Long lag = subscriptions.partitionLag(topicPartition, isolationLevel);
-            return lag == null ? OptionalLong.empty() : OptionalLong.of(lag);
+
+            // if the log end offset is not known and hence cannot return lag,
+            // issue a list offset request for that partition so that next time
+            // we may get the answer; we do not need to wait for the return value
+            // since we would not try to poll the network client synchronously
+            if (lag == null) {
+                if (subscriptions.partitionEndOffset(topicPartition, isolationLevel) == null) {
+                    log.info("Requesting the log end offset for {} in order to compute lag", topicPartition);
+                    fetcher.endOffsets(Collections.singleton(topicPartition), time.timer(0L));

Review comment:
       I modified the fetcher so that it would not wait for the future to complete, with timer(0) it would not be a blocking call. Or did I miss anything?




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