okumin commented on code in PR #6202:
URL: https://github.com/apache/hive/pull/6202#discussion_r2601529807
##########
ql/src/java/org/apache/hadoop/hive/ql/optimizer/topnkey/TopNKeyProcessor.java:
##########
@@ -71,6 +71,13 @@ public Object process(Node nd, Stack<Node> stack,
NodeProcessorCtx procCtx,
return null;
}
+ // Skip the current optimization when a simple global ORDER BY...LIMIT is
present
+ // (topN > -1 and hasOnlyOrderByLimit()).
+ // This plan structure is handled more efficiently by the specialized
'TopN In Reducer' optimization.
+ if (reduceSinkDesc.getTopN() > -1 && reduceSinkDesc.hasOnlyOrderByLimit())
{
Review Comment:
I'm also curious about the two questions in [the JIRA
ticket](https://issues.apache.org/jira/browse/HIVE-29322). I don't have an
instant answer on whether it is optimal to reuse Top-N for the global sort.
However, in my impression, it is at least suboptimal and might not be so bad.
Disclaimer: My next response might not be timely because I have to visit a
hospital every day.
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