Track scan reversals in MergeJoin

The MergeJoin struct was tracking "mergeStrategies", which were an
array of btree strategy numbers, purely for the purpose of comparing
it later against btree strategies to determine if the scan direction
was forward or reverse.  Change that.  Instead, track
"mergeReversals", an array of bool, to indicate the same without an
unfortunate assumption that a strategy number refers specifically to a
btree strategy.

Author: Mark Dilger <mark.dilger@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/E72EAA49-354D-4C2E-8EB9-255197F55330@enterprisedb.com

2 files changed, 11 insertions, 16 deletions

diff --git a/src/backend/executor/nodeMergejoin.c b/src/backend/executor/nodeMergejoin.c
index 29c54fcd753..b593905978b 100644
--- a/src/backend/executor/nodeMergejoin.c
+++ b/src/backend/executor/nodeMergejoin.c
@@ -175,7 +175,7 @@ static MergeJoinClause
 MJExamineQuals(List *mergeclauses,
 			   Oid *mergefamilies,
 			   Oid *mergecollations,
-			   int *mergestrategies,
+			   bool *mergereversals,
 			   bool *mergenullsfirst,
 			   PlanState *parent)
 {
@@ -193,7 +193,7 @@ MJExamineQuals(List *mergeclauses,
 		MergeJoinClause clause = &clauses[iClause];
 		Oid			opfamily = mergefamilies[iClause];
 		Oid			collation = mergecollations[iClause];
-		StrategyNumber opstrategy = mergestrategies[iClause];
+		bool		reversed = mergereversals[iClause];
 		bool		nulls_first = mergenullsfirst[iClause];
 		int			op_strategy;
 		Oid			op_lefttype;
@@ -212,12 +212,7 @@ MJExamineQuals(List *mergeclauses,
 		/* Set up sort support data */
 		clause->ssup.ssup_cxt = CurrentMemoryContext;
 		clause->ssup.ssup_collation = collation;
-		if (opstrategy == BTLessStrategyNumber)
-			clause->ssup.ssup_reverse = false;
-		else if (opstrategy == BTGreaterStrategyNumber)
-			clause->ssup.ssup_reverse = true;
-		else					/* planner screwed up */
-			elog(ERROR, "unsupported mergejoin strategy %d", opstrategy);
+		clause->ssup.ssup_reverse = reversed;
 		clause->ssup.ssup_nulls_first = nulls_first;
 
 		/* Extract the operator's declared left/right datatypes */
@@ -1608,7 +1603,7 @@ ExecInitMergeJoin(MergeJoin *node, EState *estate, int eflags)
 	mergestate->mj_Clauses = MJExamineQuals(node->mergeclauses,
 											node->mergeFamilies,
 											node->mergeCollations,
-											node->mergeStrategies,
+											node->mergeReversals,
 											node->mergeNullsFirst,
 											(PlanState *) mergestate);
 
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index bd54a0d032d..f2ed0d81f61 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -252,7 +252,7 @@ static MergeJoin *make_mergejoin(List *tlist,
 								 List *mergeclauses,
 								 Oid *mergefamilies,
 								 Oid *mergecollations,
-								 int *mergestrategies,
+								 bool *mergereversals,
 								 bool *mergenullsfirst,
 								 Plan *lefttree, Plan *righttree,
 								 JoinType jointype, bool inner_unique,
@@ -4451,7 +4451,7 @@ create_mergejoin_plan(PlannerInfo *root,
 	int			nClauses;
 	Oid		   *mergefamilies;
 	Oid		   *mergecollations;
-	int		   *mergestrategies;
+	bool	   *mergereversals;
 	bool	   *mergenullsfirst;
 	PathKey    *opathkey;
 	EquivalenceClass *opeclass;
@@ -4625,7 +4625,7 @@ create_mergejoin_plan(PlannerInfo *root,
 	Assert(nClauses == list_length(best_path->path_mergeclauses));
 	mergefamilies = (Oid *) palloc(nClauses * sizeof(Oid));
 	mergecollations = (Oid *) palloc(nClauses * sizeof(Oid));
-	mergestrategies = (int *) palloc(nClauses * sizeof(int));
+	mergereversals = (bool *) palloc(nClauses * sizeof(bool));
 	mergenullsfirst = (bool *) palloc(nClauses * sizeof(bool));
 
 	opathkey = NULL;
@@ -4752,7 +4752,7 @@ create_mergejoin_plan(PlannerInfo *root,
 		/* OK, save info for executor */
 		mergefamilies[i] = opathkey->pk_opfamily;
 		mergecollations[i] = opathkey->pk_eclass->ec_collation;
-		mergestrategies[i] = opathkey->pk_strategy;
+		mergereversals[i] = (opathkey->pk_strategy == BTGreaterStrategyNumber ? true : false);
 		mergenullsfirst[i] = opathkey->pk_nulls_first;
 		i++;
 	}
@@ -4772,7 +4772,7 @@ create_mergejoin_plan(PlannerInfo *root,
 							   mergeclauses,
 							   mergefamilies,
 							   mergecollations,
-							   mergestrategies,
+							   mergereversals,
 							   mergenullsfirst,
 							   outer_plan,
 							   inner_plan,
@@ -6104,7 +6104,7 @@ make_mergejoin(List *tlist,
 			   List *mergeclauses,
 			   Oid *mergefamilies,
 			   Oid *mergecollations,
-			   int *mergestrategies,
+			   bool *mergereversals,
 			   bool *mergenullsfirst,
 			   Plan *lefttree,
 			   Plan *righttree,
@@ -6123,7 +6123,7 @@ make_mergejoin(List *tlist,
 	node->mergeclauses = mergeclauses;
 	node->mergeFamilies = mergefamilies;
 	node->mergeCollations = mergecollations;
-	node->mergeStrategies = mergestrategies;
+	node->mergeReversals = mergereversals;
 	node->mergeNullsFirst = mergenullsfirst;
 	node->join.jointype = jointype;
 	node->join.inner_unique = inner_unique;