KNNGIST, otherwise known as order-by-operator support for GIST.

This commit represents a rather heavily editorialized version of
Teodor's builtin_knngist_itself-0.8.2 and builtin_knngist_proc-0.8.1
patches.  I redid the opclass API to add a separate Distance method
instead of turning the Consistent method into an illogical mess,
fixed some bit-rot in the rbtree interfaces, and generally worked over
the code style and comments.

There's still no non-code documentation to speak of, but I'll work on
that separately.  Some contrib-module changes are also yet to come
(right now, point <-> point is the only KNN-ified operator).

Teodor Sigaev and Tom Lane

1 files changed, 10 insertions, 0 deletions

diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 8c2dbc940f4..d6aaea2162d 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -1030,6 +1030,9 @@ gistnewroot(Relation r, Buffer buffer, IndexTuple *itup, int len, ItemPointer ke
 	END_CRIT_SECTION();
 }
 
+/*
+ * Fill a GISTSTATE with information about the index
+ */
 void
 initGISTstate(GISTSTATE *giststate, Relation index)
 {
@@ -1064,6 +1067,13 @@ initGISTstate(GISTSTATE *giststate, Relation index)
 		fmgr_info_copy(&(giststate->equalFn[i]),
 					   index_getprocinfo(index, i + 1, GIST_EQUAL_PROC),
 					   CurrentMemoryContext);
+		/* opclasses are not required to provide a Distance method */
+		if (OidIsValid(index_getprocid(index, i + 1, GIST_DISTANCE_PROC)))
+			fmgr_info_copy(&(giststate->distanceFn[i]),
+						   index_getprocinfo(index, i + 1, GIST_DISTANCE_PROC),
+						   CurrentMemoryContext);
+		else
+			giststate->distanceFn[i].fn_oid = InvalidOid;
 	}
 }