Change SearchSysCache coding conventions so that a reference count is

maintained for each cache entry.  A cache entry will not be freed until
the matching ReleaseSysCache call has been executed.  This eliminates
worries about cache entries getting dropped while still in use.  See
my posting to pg-hackers of even date for more info.

src/backend/nodes/makefuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/makefuncs.c,v 1.22 2000/08/08 15:41:24 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/makefuncs.c,v 1.23 2000/11/16 22:30:23 tgl Exp $
  *
  * NOTES
  *	  Creator functions in POSTGRES 4.2 are generated automatically. Most of
@@ -20,7 +20,10 @@
  *	  Andrew Yu			Oct 20, 1994	file creation
  */
 #include "postgres.h"
+
 #include "nodes/makefuncs.h"
+#include "utils/lsyscache.h"
+
 
 /*
  * makeOper -
@@ -143,6 +146,26 @@ makeConst(Oid consttype,
 	return cnst;
 }
 
+/*
+ * makeNullConst -
+ *	  creates a Const node representing a NULL of the specified type
+ */
+Const *
+makeNullConst(Oid consttype)
+{
+	int16		typLen;
+	bool		typByVal;
+
+	get_typlenbyval(consttype, &typLen, &typByVal);
+	return makeConst(consttype,
+					 (int) typLen,
+					 (Datum) 0,
+					 true,
+					 typByVal,
+					 false,
+					 false);
+}
+
 /*
  * makeAttr -
  *	  creates an Attr node