Add COST and ROWS options to CREATE/ALTER FUNCTION, plus underlying pg_proc

columns procost and prorows, to allow simple user adjustment of the estimated
cost of a function call, as well as control of the estimated number of rows
returned by a set-returning function.  We might eventually wish to extend this
to allow function-specific estimation routines, but there seems to be
consensus that we should try a simple constant estimate first.  In particular
this provides a relatively simple way to control the order in which different
WHERE clauses are applied in a plan node, which is a Good Thing in view of the
fact that the recent EquivalenceClass planner rewrite made that much less
predictable than before.

src/backend/utils/Gen_fmgrtab.sh

@@ -9,7 +9,7 @@
 #
 #
 # IDENTIFICATION
-#    $PostgreSQL: pgsql/src/backend/utils/Gen_fmgrtab.sh,v 1.34 2007/01/05 22:19:39 momjian Exp $
+#    $PostgreSQL: pgsql/src/backend/utils/Gen_fmgrtab.sh,v 1.35 2007/01/22 01:35:21 tgl Exp $
 #
 #-------------------------------------------------------------------------
 
@@ -72,6 +72,8 @@ trap 'echo "Caught signal." ; cleanup ; exit 1' 1 2 15
 #
 # Generate the file containing raw pg_proc tuple data
 # (but only for "internal" language procedures...).
+# Basically we strip off the DATA macro call, leaving procedure OID as $1
+# and all the pg_proc field values as $2, $3, etc on each line.
 #
 # Note assumption here that prolang == $5 and INTERNALlanguageId == 12.
 #
@@ -202,15 +204,15 @@ FuNkYfMgRtAbStUfF
 # may seem tedious, but avoid the temptation to write a quick x?y:z
 # conditional expression instead.  Not all awks have conditional expressions.
 #
-# Note assumptions here that prosrc == $(NF-2), pronargs == $11,
-# proisstrict == $8, proretset == $9
+# Note assumptions here that prosrc == $(NF-2), pronargs == $13,
+# proisstrict == $10, proretset == $11
 
 $AWK 'BEGIN {
     Bool["t"] = "true"
     Bool["f"] = "false"
 }
 { printf ("  { %d, \"%s\", %d, %s, %s, %s },\n"), \
-	$1, $(NF-2), $11, Bool[$8], Bool[$9], $(NF-2)
+	$1, $(NF-2), $13, Bool[$10], Bool[$11], $(NF-2)
 }' $SORTEDFILE >> "$$-$TABLEFILE"
 
 if [ $? -ne 0 ]; then

src/backend/utils/cache/lsyscache.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/cache/lsyscache.c,v 1.145 2007/01/21 00:57:15 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/cache/lsyscache.c,v 1.146 2007/01/22 01:35:21 tgl Exp $
  *
  * NOTES
  *	  Eventually, the index information should go through here, too.
@@ -1295,6 +1295,48 @@ func_volatile(Oid funcid)
 	return result;
 }
 
+/*
+ * get_func_cost
+ *		Given procedure id, return the function's procost field.
+ */
+float4
+get_func_cost(Oid funcid)
+{
+	HeapTuple	tp;
+	float4		result;
+
+	tp = SearchSysCache(PROCOID,
+						ObjectIdGetDatum(funcid),
+						0, 0, 0);
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for function %u", funcid);
+
+	result = ((Form_pg_proc) GETSTRUCT(tp))->procost;
+	ReleaseSysCache(tp);
+	return result;
+}
+
+/*
+ * get_func_rows
+ *		Given procedure id, return the function's prorows field.
+ */
+float4
+get_func_rows(Oid funcid)
+{
+	HeapTuple	tp;
+	float4		result;
+
+	tp = SearchSysCache(PROCOID,
+						ObjectIdGetDatum(funcid),
+						0, 0, 0);
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for function %u", funcid);
+
+	result = ((Form_pg_proc) GETSTRUCT(tp))->prorows;
+	ReleaseSysCache(tp);
+	return result;
+}
+
 /*				---------- RELATION CACHE ----------					 */
 
 /*