2 files changed, 91 insertions, 0 deletions

diff --git a/src/backend/utils/sort/sortsupport.c b/src/backend/utils/sort/sortsupport.c
index fcfe6e831a1..c436fbb4ce1 100644
--- a/src/backend/utils/sort/sortsupport.c
+++ b/src/backend/utils/sort/sortsupport.c
@@ -15,6 +15,7 @@
 
 #include "postgres.h"
 
+#include "access/gist.h"
 #include "access/nbtree.h"
 #include "catalog/pg_am.h"
 #include "fmgr.h"
@@ -175,3 +176,36 @@ PrepareSortSupportFromIndexRel(Relation indexRel, int16 strategy,
 
 	FinishSortSupportFunction(opfamily, opcintype, ssup);
 }
+
+/*
+ * Fill in SortSupport given a GiST index relation
+ *
+ * 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 (always false for GiST index build), as well as
+ * the comparator function pointer.
+ */
+void
+PrepareSortSupportFromGistIndexRel(Relation indexRel, SortSupport ssup)
+{
+	Oid			opfamily = indexRel->rd_opfamily[ssup->ssup_attno - 1];
+	Oid			opcintype = indexRel->rd_opcintype[ssup->ssup_attno - 1];
+	Oid			sortSupportFunction;
+
+	Assert(ssup->comparator == NULL);
+
+	if (indexRel->rd_rel->relam != GIST_AM_OID)
+		elog(ERROR, "unexpected non-gist AM: %u", indexRel->rd_rel->relam);
+	ssup->ssup_reverse = false;
+
+	/*
+	 * Look up the sort support function. This is simpler than for B-tree
+	 * indexes because we don't support the old-style btree comparators.
+	 */
+	sortSupportFunction = get_opfamily_proc(opfamily, opcintype, opcintype,
+											GIST_SORTSUPPORT_PROC);
+	if (!OidIsValid(sortSupportFunction))
+		elog(ERROR, "missing support function %d(%u,%u) in opfamily %u",
+			 GIST_SORTSUPPORT_PROC, opcintype, opcintype, opfamily);
+	OidFunctionCall1(sortSupportFunction, PointerGetDatum(ssup));
+}
diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c
index cbda911f465..d0cc04a878a 100644
--- a/src/backend/utils/sort/tuplesort.c
+++ b/src/backend/utils/sort/tuplesort.c
@@ -1168,6 +1168,63 @@ tuplesort_begin_index_hash(Relation heapRel,
 }
 
 Tuplesortstate *
+tuplesort_begin_index_gist(Relation heapRel,
+						   Relation indexRel,
+						   int workMem,
+						   SortCoordinate coordinate,
+						   bool randomAccess)
+{
+	Tuplesortstate *state = tuplesort_begin_common(workMem, coordinate,
+												   randomAccess);
+	MemoryContext oldcontext;
+	int			i;
+
+	oldcontext = MemoryContextSwitchTo(state->sortcontext);
+
+#ifdef TRACE_SORT
+	if (trace_sort)
+		elog(LOG,
+			 "begin index sort: workMem = %d, randomAccess = %c",
+			 workMem, randomAccess ? 't' : 'f');
+#endif
+
+	state->nKeys = IndexRelationGetNumberOfKeyAttributes(indexRel);
+
+	state->comparetup = comparetup_index_btree;
+	state->copytup = copytup_index;
+	state->writetup = writetup_index;
+	state->readtup = readtup_index;
+
+	state->heapRel = heapRel;
+	state->indexRel = indexRel;
+
+	/* Prepare SortSupport data for each column */
+	state->sortKeys = (SortSupport) palloc0(state->nKeys *
+											sizeof(SortSupportData));
+
+	for (i = 0; i < state->nKeys; i++)
+	{
+		SortSupport sortKey = state->sortKeys + i;
+
+		sortKey->ssup_cxt = CurrentMemoryContext;
+		sortKey->ssup_collation = indexRel->rd_indcollation[i];
+		sortKey->ssup_nulls_first = false;
+		sortKey->ssup_attno = i + 1;
+		/* Convey if abbreviation optimization is applicable in principle */
+		sortKey->abbreviate = (i == 0);
+
+		AssertState(sortKey->ssup_attno != 0);
+
+		/* Look for a sort support function */
+		PrepareSortSupportFromGistIndexRel(indexRel, sortKey);
+	}
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return state;
+}
+
+Tuplesortstate *
 tuplesort_begin_datum(Oid datumType, Oid sortOperator, Oid sortCollation,
 					  bool nullsFirstFlag, int workMem,
 					  SortCoordinate coordinate, bool randomAccess)