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.

1 files changed, 43 insertions, 1 deletions

diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index d2041a507d0..c449ad6e742 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/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 ----------					 */
 
 /*