vpapavas commented on code in PR #12555:
URL: https://github.com/apache/kafka/pull/12555#discussion_r960845326
##########
streams/src/main/java/org/apache/kafka/streams/kstream/internals/InternalStreamsBuilder.java:
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@@ -356,6 +381,95 @@ private void mergeDuplicateSourceNodes() {
}
}
+ /**
+ * If the join is a self-join, remove the node KStreamJoinWindow
corresponding to the
+ */
+ @SuppressWarnings("unchecked")
+ private void rewriteSelfJoin(final GraphNode currentNode, final
Set<GraphNode> visited) {
+ visited.add(currentNode);
+ if (currentNode instanceof StreamStreamJoinNode &&
isSelfJoin(currentNode)) {
+ ((StreamStreamJoinNode) currentNode).setSelfJoin();
+ // Remove JoinOtherWindowed node
+ final GraphNode parent =
currentNode.parentNodes().stream().findFirst().get();
+ GraphNode left = null, right = null;
+ for (final GraphNode child: parent.children()) {
+ if (child instanceof ProcessorGraphNode
+ && isStreamJoinWindowNode((ProcessorGraphNode) child)) {
+ if (left == null) {
+ left = child;
+ } else {
+ right = child;
+ }
+ }
+ }
+ // Sanity check
+ if (left != null && right != null && left.buildPriority() <
right.buildPriority()) {
+ parent.removeChild(right);
+ }
+ }
+ for (final GraphNode child: currentNode.children()) {
+ if (!visited.contains(child)) {
+ rewriteSelfJoin(child, visited);
Review Comment:
We can have n-way self-joins but they won't get optimized, only the first
one will get optimized. However, we can have topologies that have more than one
self-joins, not n-way but independent pairs. And all of them can and should be
optimized. I added a test case in
`InternalStreamsBuilderTest:shouldMarkAllStreamStreamJoinsAsSelfJoin`
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