[GitHub] [kafka] chia7712 commented on a change in pull request #10096: KAFKA-12268: Make early poll return opt-in

[GitBox <gi...@apache.org>]

chia7712 commented on a change in pull request #10096:
URL: https://github.com/apache/kafka/pull/10096#discussion_r573459714



##########
File path: streams/src/main/java/org/apache/kafka/streams/StreamsConfig.java
##########
@@ -1201,6 +1201,9 @@ private void verifyMaxInFlightRequestPerConnection(final Object maxInFlightReque
         // disable auto topic creation
         consumerProps.put(ConsumerConfig.ALLOW_AUTO_CREATE_TOPICS_CONFIG, "false");
 
+        // enable early return on metadata
+        consumerProps.put(ConsumerConfig.LONG_POLL_MODE_CONFIG, ConsumerConfig.LONG_POLL_RETURN_ON_RECORDS);

Review comment:
       It should be `LONG_POLL_RETURN_ON_RESPONSE` rather than `LONG_POLL_RETURN_ON_RECORDS`

##########
File path: clients/src/main/java/org/apache/kafka/clients/consumer/KafkaConsumer.java
##########
@@ -1236,7 +1243,17 @@ public void assign(Collection<TopicPartition> partitions) {
                 }
 
                 final FetchedRecords<K, V> records = pollForFetches(timer);
-                if (!records.isEmpty()) {
+
+                // We only need to save off the metadata if we are NOT supposed to return early on metadata-only responses
+                if (!longPollExitEarlyOnMetadata) {

Review comment:
       How about updating `nullableSeenMetadata` only if we don't return records?
   ```java
   if (longPollShouldReturn(records)) { 
    ...
   } else {
     if (nullableSeenMetadata == null) {
       nullableSeenMetadata = new HashMap<>(records.metadata());
     } else {
       nullableSeenMetadata.putAll(records.metadata());
     }
   }
   ```
   
   The benefit from above code is that we don't need to handle duplicate metadata which exists on both `FetchedRecords` and `nullableSeenMetadata` when it succeed to get records and metadata in first loop.
    




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