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

Author: petere

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);
 

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;

src/include/nodes/plannodes.h

@@ -850,7 +850,7 @@ typedef struct MergeJoin
 	Oid		   *mergeCollations pg_node_attr(array_size(mergeclauses));
 
 	/* per-clause ordering (ASC or DESC) */
-	int		   *mergeStrategies pg_node_attr(array_size(mergeclauses));
+	bool	   *mergeReversals pg_node_attr(array_size(mergeclauses));
 
 	/* per-clause nulls ordering */
 	bool	   *mergeNullsFirst pg_node_attr(array_size(mergeclauses));