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For some context, when building a streams application, the optimizer keeps track of the key-changing operations and any repartition nodes that are descendants of the key-changer. During the optimization phase (if enabled), any repartition nodes are logically collapsed into one. The optimizer updates the graph by inserting the single repartition node between the key-changing node and its first child node. This graph update process is done by searching for a node that has the key-changing node as one of its direct parents, and the search starts from the repartition node, going up in the parent hierarchy. The one exception to this rule is if there is a merge node that is a descendant of the key-changing node, then during the optimization phase, the map tracking key-changers to repartition nodes is updated to have the merge node as the key. Then the optimization process updates the graph to place the single repartition node between the merge node and its first child node. The error in KAFKA-9739 occurred because there was an assumption that the repartition nodes are children of the merge node. But in the topology from KAFKA-9739, the repartition node was a parent of the merge node. So when attempting to find the first child of the merge node, nothing was found (obviously) resulting in StreamException(Found a null keyChangingChild node for..) This PR fixes this bug by first checking that all repartition nodes for optimization are children of the merge node. This PR includes a test with the topology from KAFKA-9739. Reviewers: John Roesler <john@confluent.io>
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This is a port of #8400 for the 2.5 branch
Summary of testing strategy (including rationale)
for the feature or bug fix. Unit and/or integration
tests are expected for any behaviour change and
system tests should be considered for larger changes.
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