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

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

ijuma commented on a change in pull request #10096:
URL: https://github.com/apache/kafka/pull/10096#discussion_r573811199



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File path: clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerConfig.java
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@@ -71,6 +71,21 @@
     /** <code>max.poll.interval.ms</code> */
     public static final String MAX_POLL_INTERVAL_MS_CONFIG = CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG;
     private static final String MAX_POLL_INTERVAL_MS_DOC = CommonClientConfigs.MAX_POLL_INTERVAL_MS_DOC;
+
+    /** <code>long.poll.mode</code> */
+    public static final String LONG_POLL_RETURN_ON_RECORDS = "return_on_records";
+    public static final String LONG_POLL_RETURN_ON_RESPONSE = "return_on_response";
+    public static final String LONG_POLL_MODE_CONFIG = "long.poll.mode";
+    public static final String LONG_POLL_MODE_DOC = "Whether a call to Consumer#poll(...) should block until" +
+        " records are received (return_on_records), or should return early if a metadata-only response is received" +
+        " from the brokers (return_on_metadata). The 'return_on_records' mode is the default, and it matches prior" +
+        " behavior. The 'return_on_response' mode allows callers to witness topic metadata changes via" +
+        " ConsumerRecords#metadata() as soon as they are received in a fetch response, even if there are no records" +
+        " included in the response. Callers who are only interested in seeing records should leave the default in" +
+        " place, and callers who are interested in maintaining fresh local information about the current lag should" +
+        " enable 'return_on_response'." +
+        " Note that the Consumer metrics are always updated upon receipt of the fetch responses.";

Review comment:
       Hmm, this doesn't seem great.




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