[GitHub] [kafka] guozhangwang commented on a diff in pull request #12555: Optimize self-join

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

guozhangwang commented on code in PR #12555:
URL: https://github.com/apache/kafka/pull/12555#discussion_r960983275


##########
streams/src/main/java/org/apache/kafka/streams/kstream/internals/InternalStreamsBuilder.java:
##########
@@ -270,16 +272,20 @@ private void maybeAddNodeForOptimizationMetadata(final GraphNode node) {
 
     // use this method for testing only
     public void buildAndOptimizeTopology() {
-        buildAndOptimizeTopology(false);
+        buildAndOptimizeTopology(false, false);
     }
 
-    public void buildAndOptimizeTopology(final boolean optimizeTopology) {
+    public void buildAndOptimizeTopology(
+        final boolean optimizeTopology, final boolean optimizeSelfJoin) {
 
         mergeDuplicateSourceNodes();
         if (optimizeTopology) {
             LOG.debug("Optimizing the Kafka Streams graph for repartition nodes");
             optimizeKTableSourceTopics();
             maybeOptimizeRepartitionOperations();
+            if (optimizeSelfJoin) {

Review Comment:
   Hmm.. for case 2), the logical plan would be like:
   
   ```
   root -> source1
   root -> source2
   source1 -> join-window1
   source2 -> join-window2
   source1,source2 -> stream-join
   ```
   
   Is that right?
   
   For case 3), since we are not re-assigning the result of `mapValues` to stream` it should just be a no-op right? The logical plan would be like:
   
   ```
   root -> source1
   root -> source2
   source1 -> join-window1
   source1 -> map-values1
   source2 -> join-window2
   source1,source2 -> stream-join
   ```
   
   Should that be considered optimizable as well?



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