From f5d29489ab69ad7a6ab6ad18ebc0ea5e498d37b7 Mon Sep 17 00:00:00 2001
From: aviralgarg05 <gargaviral99@gmail.com>
Date: Mon, 25 May 2026 23:26:55 +0530
Subject: [PATCH] orca: keep parallel semi joins from rewriting to dedup

---
 .../src/xforms/CXformLeftSemiJoin2InnerJoin.cpp   | 15 +++++++++++++++
 .../CXformLeftSemiJoin2InnerJoinUnderGb.cpp       | 15 +++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoin.cpp b/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoin.cpp
index 434dc8590b4..b6c4ad350b1 100644
--- a/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoin.cpp
+++ b/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoin.cpp
@@ -24,6 +24,11 @@
 #include "gpopt/operators/CPredicateUtils.h"
 #include "gpopt/operators/CScalarProjectList.h"
 
+namespace gpdb
+{
+	bool IsParallelModeOK(void);
+}
+
 
 
 using namespace gpopt;
@@ -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;
+	}
+
 	if (exprhdl.HasOuterRefs() || exprhdl.DeriveHasSubquery(2))
 	{
 		return ExfpNone;
diff --git a/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoinUnderGb.cpp b/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoinUnderGb.cpp
index f5f225572ee..b6755b36b89 100644
--- a/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoinUnderGb.cpp
+++ b/src/backend/gporca/libgpopt/src/xforms/CXformLeftSemiJoin2InnerJoinUnderGb.cpp
@@ -24,6 +24,11 @@
 #include "gpopt/operators/CPredicateUtils.h"
 #include "gpopt/operators/CScalarProjectList.h"
 
+namespace gpdb
+{
+	bool IsParallelModeOK(void);
+}
+
 using namespace gpopt;
 
 //---------------------------------------------------------------------------
@@ -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;