[GitHub] [flink] fapaul commented on a change in pull request #18412: [FLINK-25696][datastream] Introduce metadataConsumer to InitContext in Sink

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fapaul commented on a change in pull request #18412:
URL: https://github.com/apache/flink/pull/18412#discussion_r792434481



##########
File path: flink-core/src/main/java/org/apache/flink/api/connector/sink/Sink.java
##########
@@ -170,6 +171,15 @@
          * previous execution.
          */
         OptionalLong getRestoredCheckpointId();
+
+        /**
+         * Returns a metadata consumer, the {@link SinkWriter} can publish metadata events of type
+         * {@link MetaT} to the consumer. The consumer can accept metadata events in an asynchronous

Review comment:
       If you want to recommend not executing the metadata consumer as part of the mailbox you should make it clearer.
   
   ```suggestion
            * <p> It is recommended to use a separate thread pool to publish the metadata because enqueuing a lot of these messages in the mailbox may lead to a performance decrease.
   ```

##########
File path: flink-core/src/main/java/org/apache/flink/api/connector/sink2/Sink.java
##########
@@ -105,5 +107,14 @@
          * Provides a view on this context as a {@link SerializationSchema.InitializationContext}.
          */
         SerializationSchema.InitializationContext asSerializationSchemaInitializationContext();
+
+        /**
+         * Returns a metadata consumer, the {@link SinkWriter} can publish metadata events of type
+         * {@link MetaT} to the consumer. The consumer can accept metadata events in an asynchronous
+         * thread, and the {@link Consumer#accept} method is executed very fast.
+         */
+        default <MetaT> Optional<Consumer<MetaT>> metadataConsumer() {

Review comment:
       I'd mark this `@Experimental` to leave some room to change the threading model later if necessary.




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