Indhumathi27 commented on code in PR #6202:
URL: https://github.com/apache/hive/pull/6202#discussion_r2800027509
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ql/src/java/org/apache/hadoop/hive/ql/parse/TezCompiler.java:
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@@ -1322,6 +1325,54 @@ private static void
runTopNKeyOptimization(OptimizeTezProcContext procCtx)
ogw.startWalking(topNodes, null);
}
+ /*
+ * Build the ReduceSink matching pattern used by TopNKey optimization.
+ *
+ * For ORDER BY / LIMIT queries that do not involve GROUP BY or JOIN,
+ * applying TopNKey results in a performance regression. ReduceSink
+ * operators created only for ordering must therefore be excluded from
+ * TopNKey.
+ *
+ * When ORDER BY or LIMIT is present, restrict TopNKey to ReduceSink
+ * operators that originate from GROUP BY, JOIN, MAPJOIN, LATERAL VIEW
+ * JOIN or PTF query shapes. SELECT and FILTER operators may appear in
+ * between.
+ */
+ private static String buildTopNKeyRegexPattern(OptimizeTezProcContext
procCtx) {
+ String reduceSinkOp = ReduceSinkOperator.getOperatorName() + "%";
+
+ boolean hasOrderOrLimit =
+ procCtx.parseContext.getQueryProperties().hasLimit() ||
+ procCtx.parseContext.getQueryProperties().hasOrderBy();
Review Comment:
@zabetak Many thanks for the detailed feedback and helpful suggestions —
they provide a very clear direction for improving the evaluation. At the moment
I am a bit limited in bandwidth, but I plan to take this up and extend the
experimental setup along the proposed lines when I have more time. Thanks again
for the valuable input and the offer to collaborate on the write-up.
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