Build out the planner support function infrastructure.

Add support function requests for estimating the selectivity, cost,
and number of result rows (if a SRF) of the target function.

The lack of a way to estimate selectivity of a boolean-returning
function in WHERE has been a recognized deficiency of the planner
since Berkeley days.  This commit finally fixes it.

In addition, non-constant estimates of cost and number of output
rows are now possible.  We still fall back to looking at procost
and prorows if the support function doesn't service the request,
of course.

To make concrete use of the possibility of estimating output rowcount
for SRFs, this commit adds support functions for array_unnest(anyarray)
and the integer variants of generate_series; the lack of plausible
rowcount estimates for those, even when it's obvious to a human,
has been a repeated subject of complaints.  Obviously, much more
could now be done in this line, but I'm mostly just trying to get
the infrastructure in place.

Discussion: https://postgr.es/m/15193.1548028093@sss.pgh.pa.us

1 files changed, 16 insertions, 29 deletions

diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index fba0ee8b847..e88c45d268a 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -1605,41 +1605,28 @@ get_func_leakproof(Oid funcid)
 }
 
 /*
- * get_func_cost
- *		Given procedure id, return the function's procost field.
- */
-float4
-get_func_cost(Oid funcid)
-{
-	HeapTuple	tp;
-	float4		result;
-
-	tp = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
-	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.
+ * get_func_support
+ *
+ *		Returns the support function OID associated with a given function,
+ *		or InvalidOid if there is none.
  */
-float4
-get_func_rows(Oid funcid)
+RegProcedure
+get_func_support(Oid funcid)
 {
 	HeapTuple	tp;
-	float4		result;
 
 	tp = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
-	if (!HeapTupleIsValid(tp))
-		elog(ERROR, "cache lookup failed for function %u", funcid);
+	if (HeapTupleIsValid(tp))
+	{
+		Form_pg_proc functup = (Form_pg_proc) GETSTRUCT(tp);
+		RegProcedure result;
 
-	result = ((Form_pg_proc) GETSTRUCT(tp))->prorows;
-	ReleaseSysCache(tp);
-	return result;
+		result = functup->prosupport;
+		ReleaseSysCache(tp);
+		return result;
+	}
+	else
+		return (RegProcedure) InvalidOid;
 }
 
 /*				---------- RELATION CACHE ----------					 */