1 files changed, 60 insertions, 19 deletions

diff --git a/src/backend/utils/sort/sortsupport.c b/src/backend/utils/sort/sortsupport.c
index 2240fd01001..16342f388db 100644
--- a/src/backend/utils/sort/sortsupport.c
+++ b/src/backend/utils/sort/sortsupport.c
@@ -21,6 +21,7 @@
 #include "access/nbtree.h"
 #include "fmgr.h"
 #include "utils/lsyscache.h"
+#include "utils/rel.h"
 #include "utils/sortsupport.h"
 
 
@@ -86,28 +87,14 @@ PrepareSortSupportComparisonShim(Oid cmpFunc, SortSupport ssup)
 }
 
 /*
- * Fill in SortSupport given an ordering operator (btree "<" or ">" operator).
- *
- * Caller must previously have zeroed the SortSupportData structure and then
- * filled in ssup_cxt, ssup_collation, and ssup_nulls_first.  This will fill
- * in ssup_reverse as well as the comparator function pointer.
+ * Look up and call sortsupport function to setup SortSupport comparator;
+ * or if no such function exists or it declines to set up the appropriate
+ * state, prepare a suitable shim.
  */
-void
-PrepareSortSupportFromOrderingOp(Oid orderingOp, SortSupport ssup)
+static void
+FinishSortSupportFunction(Oid opfamily, Oid opcintype, SortSupport ssup)
 {
 	Oid			sortSupportFunction;
-	Oid			opfamily;
-	Oid			opcintype;
-	int16		strategy;
-
-	Assert(ssup->comparator == NULL);
-
-	/* Find the operator in pg_amop */
-	if (!get_ordering_op_properties(orderingOp, &opfamily, &opcintype,
-									&strategy))
-		elog(ERROR, "operator %u is not a valid ordering operator",
-			 orderingOp);
-	ssup->ssup_reverse = (strategy == BTGreaterStrategyNumber);
 
 	/* Look for a sort support function */
 	sortSupportFunction = get_opfamily_proc(opfamily, opcintype, opcintype,
@@ -136,3 +123,57 @@ PrepareSortSupportFromOrderingOp(Oid orderingOp, SortSupport ssup)
 		PrepareSortSupportComparisonShim(sortFunction, ssup);
 	}
 }
+
+/*
+ * Fill in SortSupport given an ordering operator (btree "<" or ">" operator).
+ *
+ * Caller must previously have zeroed the SortSupportData structure and then
+ * filled in ssup_cxt, ssup_collation, and ssup_nulls_first.  This will fill
+ * in ssup_reverse as well as the comparator function pointer.
+ */
+void
+PrepareSortSupportFromOrderingOp(Oid orderingOp, SortSupport ssup)
+{
+	Oid			opfamily;
+	Oid			opcintype;
+	int16		strategy;
+
+	Assert(ssup->comparator == NULL);
+
+	/* Find the operator in pg_amop */
+	if (!get_ordering_op_properties(orderingOp, &opfamily, &opcintype,
+									&strategy))
+		elog(ERROR, "operator %u is not a valid ordering operator",
+			 orderingOp);
+	ssup->ssup_reverse = (strategy == BTGreaterStrategyNumber);
+
+	FinishSortSupportFunction(opfamily, opcintype, ssup);
+}
+
+/*
+ * Fill in SortSupport given an index relation, attribute, and strategy.
+ *
+ * Caller must previously have zeroed the SortSupportData structure and then
+ * filled in ssup_cxt, ssup_attno, ssup_collation, and ssup_nulls_first.  This
+ * will fill in ssup_reverse (based on the supplied strategy), as well as the
+ * comparator function pointer.
+ */
+void
+PrepareSortSupportFromIndexRel(Relation indexRel, int16 strategy,
+							   SortSupport ssup)
+{
+	Oid			opfamily = indexRel->rd_opfamily[ssup->ssup_attno - 1];
+	Oid			opcintype = indexRel->rd_opcintype[ssup->ssup_attno - 1];
+
+	Assert(ssup->comparator == NULL);
+
+	/* Find the operator in pg_amop */
+	if (indexRel->rd_rel->relam != BTREE_AM_OID)
+		elog(ERROR, "unexpected non-btree AM: %u", indexRel->rd_rel->relam);
+	if (strategy != BTGreaterStrategyNumber &&
+		strategy != BTLessStrategyNumber)
+		elog(ERROR, "unexpected sort support strategy: %d", strategy);
+	ssup->ssup_reverse = (strategy == BTGreaterStrategyNumber);
+
+	FinishSortSupportFunction(opfamily, opcintype, ssup);
+}