Create core infrastructure for KNNGIST.

This is a heavily revised version of builtin_knngist_core-0.9.  The
ordering operators are no longer mixed in with actual quals, which would
have confused not only humans but significant parts of the planner.
Instead, ordering operators are carried separately throughout planning and
execution.

Since the API for ambeginscan and amrescan functions had to be changed
anyway, this commit takes the opportunity to rationalize that a bit.
RelationGetIndexScan no longer forces a premature index_rescan call;
instead, callers of index_beginscan must call index_rescan too.  Aside from
making the AM-side initialization logic a bit less peculiar, this has the
advantage that we do not make a useless extra am_rescan call when there are
runtime key values.  AMs formerly could not assume that the key values
passed to amrescan were actually valid; now they can.

Teodor Sigaev and Tom Lane

1 files changed, 27 insertions, 4 deletions

diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 9beae0d9ef1..cbdfe05031f 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -86,18 +86,41 @@ get_op_opfamily_strategy(Oid opno, Oid opfamily)
 }
 
 /*
+ * get_op_opfamily_sortfamily
+ *
+ *		If the operator is an ordering operator within the specified opfamily,
+ *		return its amopsortfamily OID; else return InvalidOid.
+ */
+Oid
+get_op_opfamily_sortfamily(Oid opno, Oid opfamily)
+{
+	HeapTuple	tp;
+	Form_pg_amop amop_tup;
+	Oid			result;
+
+	tp = SearchSysCache3(AMOPOPID,
+						 ObjectIdGetDatum(opno),
+						 CharGetDatum(AMOP_ORDER),
+						 ObjectIdGetDatum(opfamily));
+	if (!HeapTupleIsValid(tp))
+		return InvalidOid;
+	amop_tup = (Form_pg_amop) GETSTRUCT(tp);
+	result = amop_tup->amopsortfamily;
+	ReleaseSysCache(tp);
+	return result;
+}
+
+/*
  * get_op_opfamily_properties
  *
  *		Get the operator's strategy number and declared input data types
  *		within the specified opfamily.
  *
- * This function only considers search operators, not ordering operators.
- *
  * Caller should already have verified that opno is a member of opfamily,
  * therefore we raise an error if the tuple is not found.
  */
 void
-get_op_opfamily_properties(Oid opno, Oid opfamily,
+get_op_opfamily_properties(Oid opno, Oid opfamily, bool ordering_op,
 						   int *strategy,
 						   Oid *lefttype,
 						   Oid *righttype)
@@ -107,7 +130,7 @@ get_op_opfamily_properties(Oid opno, Oid opfamily,
 
 	tp = SearchSysCache3(AMOPOPID,
 						 ObjectIdGetDatum(opno),
-						 CharGetDatum(AMOP_SEARCH),
+						 CharGetDatum(ordering_op ? AMOP_ORDER : AMOP_SEARCH),
 						 ObjectIdGetDatum(opfamily));
 	if (!HeapTupleIsValid(tp))
 		elog(ERROR, "operator %u is not a member of opfamily %u",