Add stratnum GiST support function

This is support function 12 for the GiST AM and translates
"well-known" RT*StrategyNumber values into whatever strategy number is
used by the opclass (since no particular numbers are actually
required).  We will use this to support temporal PRIMARY
KEY/UNIQUE/FOREIGN KEY/FOR PORTION OF functionality.

This commit adds two implementations, one for internal GiST opclasses
(just an identity function) and another for btree_gist opclasses.  It
updates btree_gist from 1.7 to 1.8, adding the support function for
all its opclasses.

Author: Paul A. Jungwirth <pj@illuminatedcomputing.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: jian he <jian.universality@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CA+renyUApHgSZF9-nd-a0+OPGharLQLO=mDHcY4_qQ0+noCUVg@mail.gmail.com

1 files changed, 14 insertions, 0 deletions

diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c
index dddc08893a1..d4d08bd118f 100644
--- a/src/backend/access/gist/gistutil.c
+++ b/src/backend/access/gist/gistutil.c
@@ -23,6 +23,7 @@
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
 #include "utils/float.h"
+#include "utils/fmgrprotos.h"
 #include "utils/lsyscache.h"
 #include "utils/snapmgr.h"
 #include "utils/syscache.h"
@@ -1056,3 +1057,16 @@ gistGetFakeLSN(Relation rel)
 		return GetFakeLSNForUnloggedRel();
 	}
 }
+
+/*
+ * Returns the same number that was received.
+ *
+ * This is for GiST opclasses that use the RT*StrategyNumber constants.
+ */
+Datum
+gist_stratnum_identity(PG_FUNCTION_ARGS)
+{
+	StrategyNumber strat = PG_GETARG_UINT16(0);
+
+	PG_RETURN_UINT16(strat);
+}