zabetak commented on code in PR #6202:
URL: https://github.com/apache/hive/pull/6202#discussion_r2668171523
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ql/src/java/org/apache/hadoop/hive/ql/optimizer/topnkey/TopNKeyProcessor.java:
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@@ -111,6 +123,50 @@ public Object process(Node nd, Stack<Node> stack,
NodeProcessorCtx procCtx,
return null;
}
+ /**
+ * Returns true if the ReduceSink is only under an ORDER BY + LIMIT plan
+ * and has no GroupBy or Join operators in its upstream ancestry.
+ * This is used to disable TopNKey for pure ORDER BY LIMIT queries where
+ * LIMIT pushdown must take precedence.
+ */
+ public static boolean isOrderByLimitPath(ReduceSinkOperator rs) {
Review Comment:
Thanks for running the experiments. Ideally, it would be nice if we could
have a theoretical claim that shows that TopNKeyOptimization is useful or not
when we have simple (no GBY/JOIN etc) plan branches similarly to the analysis
that we did in the JIRA ticket for the ORDER BY LIMIT use-case.
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