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Draft: HIVE-29322: Avoid TopNKeyOperator When Map-Side LIMIT Pushdown Provides Better Pruning #6202

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Draft: HIVE-29322: Avoid TopNKeyOperator When Map-Side LIMIT Pushdown Provides Better Pruning #6202

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6 changes: 4 additions & 2 deletions ql/src/java/org/apache/hadoop/hive/ql/optimizer/topnkey/TopNKeyProcessor.java
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Original file line number Diff line number Diff line change
Expand Up @@ -66,8 +66,10 @@ public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx,
ReduceSinkOperator reduceSinkOperator = (ReduceSinkOperator) nd;
ReduceSinkDesc reduceSinkDesc = reduceSinkOperator.getConf();

// Check whether the reduce sink operator contains top n
if (reduceSinkDesc.getTopN() < 0 || !reduceSinkDesc.isOrdering()) {
// HIVE-29322: Skip creating TopNKeyOperator when LIMIT pushdown has already applied (topN != -1)
// and the query uses a single reducer with no partition columns. In this scenario,
// TopNKey offers no extra pruning benefit and only adds unnecessary processing overhead.
if (reduceSinkDesc.getTopN() > -1 || !reduceSinkDesc.isOrdering()) {
return null;
}

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