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orca: keep parallel semi joins from rewriting to dedup #1764

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orca: keep parallel semi joins from rewriting to dedup #1764

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15 changes: 15 additions & 0 deletions src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoin.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,11 @@
#include "gpopt/operators/CPredicateUtils.h"
#include "gpopt/operators/CScalarProjectList.h"

namespace gpdb
{
bool IsParallelModeOK(void);
}



using namespace gpopt;
Expand Down Expand Up @@ -63,6 +68,16 @@ CXformLeftSemiJoin2InnerJoin::CXformLeftSemiJoin2InnerJoin(CMemoryPool *mp)
CXform::EXformPromise
CXformLeftSemiJoin2InnerJoin::Exfp(CExpressionHandle &exprhdl) const
{
/*
* In parallel mode, prefer direct semi-join implementations. Rewriting a
* semi-join to an inner join plus dedup can produce unstable ORCA plans
* for parallel queries.
*/
if (gpdb::IsParallelModeOK())
{
return ExfpNone;
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@yjhjstz yjhjstz May 25, 2026

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Disabling them removes a plan candidate that may have been the cost-optimal choice even for some serial queries in a parallel-enabled session, we need to find root cause .

}

if (exprhdl.HasOuterRefs() || exprhdl.DeriveHasSubquery(2))
{
return ExfpNone;
Expand Down
15 changes: 15 additions & 0 deletions src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoinUnderGb.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,11 @@
#include "gpopt/operators/CPredicateUtils.h"
#include "gpopt/operators/CScalarProjectList.h"

namespace gpdb
{
bool IsParallelModeOK(void);
}

using namespace gpopt;

//---------------------------------------------------------------------------
Expand Down Expand Up @@ -60,6 +65,16 @@ CXformLeftSemiJoin2InnerJoinUnderGb::CXformLeftSemiJoin2InnerJoinUnderGb(
CXform::EXformPromise
CXformLeftSemiJoin2InnerJoinUnderGb::Exfp(CExpressionHandle &exprhdl) const
{
/*
* In parallel mode, prefer direct semi-join implementations. Rewriting a
* semi-join to an inner join plus dedup can produce unstable ORCA plans
* for parallel queries.
*/
if (gpdb::IsParallelModeOK())
{
return ExfpNone;
}

CColRefSet *pcrsInnerOutput = exprhdl.DeriveOutputColumns(1);
CExpression *pexprScalar = exprhdl.PexprScalarExactChild(2);
CAutoMemoryPool amp;
Expand Down