[GitHub] [kafka] soceanainn commented on a change in pull request #11470: MINOR: Update docs for producer callbacks to reflect current behaviour

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soceanainn commented on a change in pull request #11470:
URL: https://github.com/apache/kafka/pull/11470#discussion_r745122437



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File path: clients/src/main/java/org/apache/kafka/clients/producer/Callback.java
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@@ -25,10 +25,12 @@
     /**
      * A callback method the user can implement to provide asynchronous handling of request completion. This method will
      * be called when the record sent to the server has been acknowledged. When exception is not null in the callback,
-     * metadata will contain the special -1 value for all fields except for topicPartition, which will be valid.
+     * and the exception is a subclass of ApiException, metadata will be null. For all other exceptions, metadata will

Review comment:
       I don't think metadata will always be null, as the updated metadata will sometimes be passed to the user callback as far as I can see from the InterceptorCallback implementation (see [here](https://github.com/apache/kafka/blob/3.1/clients/src/main/java/org/apache/kafka/clients/producer/KafkaProducer.java#L1387-L1390)).
   
   I believe we have been seeing a mixture of null metadata + placeholder metadata in our Kafka deployment (v2.3.1), which has caused some issues for my team.




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