ORCA: add optimizer_enable_right_semi_join GUC

Adds a GUC (default on) to enable/disable GPORCA's right semi/anti hash join
xforms (CXformLeftSemiJoin2RightSemiHashJoin /
CXformLeftAntiSemiJoin2RightAntiSemiHashJoin).  When turned off, the xforms
are disabled via the standard CConfigParamMapping traceflag mechanism
(GPOPT_DISABLE_XFORM_TF), so ORCA falls back to its regular left-semi / anti
plans.

Serves both as a kill-switch for the new plan shape and as the on/off toggle
for before/after performance comparisons (e.g. TPC-H Q21).

The GUC is registered in unsync_guc_name.h (per-segment, no QD/QE sync
required), matching the other optimizer_enable_* developer GUCs.

  SET optimizer_enable_right_semi_join = off;  -- ORCA uses plain Hash Semi Join
  SET optimizer_enable_right_semi_join = on;   -- ORCA may use Hash Right Semi Join

Author: kongfanshen

src/backend/gpopt/config/CConfigParamMapping.cpp

@@ -442,6 +442,15 @@ CConfigParamMapping::PackConfigParamInBitset(
 		hash_join_bitste->Release();
 	}
 
+	// disable right semi/anti hash join (Mark Join) xforms if the GUC is off
+	if (!optimizer_enable_right_semi_join)
+	{
+		traceflag_bitset->ExchangeSet(
+			GPOPT_DISABLE_XFORM_TF(CXform::ExfLeftSemiJoin2RightSemiHashJoin));
+		traceflag_bitset->ExchangeSet(GPOPT_DISABLE_XFORM_TF(
+			CXform::ExfLeftAntiSemiJoin2RightAntiSemiHashJoin));
+	}
+
 	if (!optimizer_enable_dynamictablescan)
 	{
 		// disable dynamic table scan if the corresponding GUC is turned off

src/backend/utils/misc/guc_gp.c

@@ -352,6 +352,7 @@ bool		optimizer_enable_dml;
 bool		optimizer_enable_dml_constraints;
 bool		optimizer_enable_master_only_queries;
 bool		optimizer_enable_hashjoin;
+bool		optimizer_enable_right_semi_join = true;
 bool		optimizer_enable_dynamictablescan;
 bool		optimizer_enable_dynamicindexscan;
 bool		optimizer_enable_dynamicindexonlyscan;
@@ -2354,6 +2355,17 @@ struct config_bool ConfigureNamesBool_gp[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"optimizer_enable_right_semi_join", PGC_USERSET, DEVELOPER_OPTIONS,
+			gettext_noop("Enables the optimizer's use of right semi/anti hash join plans."),
+			NULL,
+			GUC_NO_SHOW_ALL | GUC_NOT_IN_SAMPLE
+		},
+		&optimizer_enable_right_semi_join,
+		true,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"optimizer_enable_dynamictablescan", PGC_USERSET, DEVELOPER_OPTIONS,
 			gettext_noop("Enables the optimizer's use of plans with dynamic table scan."),

src/include/utils/guc.h

@@ -540,6 +540,7 @@ extern bool	optimizer_enable_dml_constraints;
 extern bool optimizer_enable_direct_dispatch;
 extern bool optimizer_enable_master_only_queries;
 extern bool optimizer_enable_hashjoin;
+extern bool optimizer_enable_right_semi_join;
 extern bool optimizer_enable_dynamictablescan;
 extern bool optimizer_enable_dynamicindexscan;
 extern bool optimizer_enable_dynamicindexonlyscan;

src/include/utils/unsync_guc_name.h

@@ -424,6 +424,7 @@
 		"optimizer_discard_redistribute_hashjoin",
 		"optimizer_enable_indexjoin",
 		"optimizer_enable_indexonlyscan",
+		"optimizer_enable_right_semi_join",
 		"optimizer_enable_indexscan",
 		"optimizer_enable_master_only_queries",
 		"optimizer_enable_materialize",