Tweak set_rel_width() to avoid redundant executions of getrelid().

In very large queries this accounts for a noticeable fraction of
planning time.  Per an example from Greg Stark.

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index ff5bb7833727a95eb2eb28b9f35bd74b66a433d5..42a5520b974ebf0f0947923534e349f00be16d69 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -54,7 +54,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.179 2007/03/27 23:21:09 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.180 2007/04/21 02:41:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2357,12 +2357,22 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 {
    int32       tuple_width = 0;
    ListCell   *tllist;
+   Oid         rel_reloid;
+
+   /*
+    * Usually (perhaps always), all the Vars have the same reloid, so we can
+    * save some redundant list-searching by doing getrelid just once.
+    */
+   if (rel->relid > 0)
+       rel_reloid = getrelid(rel->relid, root->parse->rtable);
+   else
+       rel_reloid = InvalidOid;            /* probably can't happen */
 
    foreach(tllist, rel->reltargetlist)
    {
        Var        *var = (Var *) lfirst(tllist);
        int         ndx;
-       Oid         relid;
+       Oid         var_reloid;
        int32       item_width;
 
        /* For now, punt on whole-row child Vars */
@@ -2383,10 +2393,14 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
            continue;
        }
 
-       relid = getrelid(var->varno, root->parse->rtable);
-       if (relid != InvalidOid)
+       if (var->varno == rel->relid)
+           var_reloid = rel_reloid;
+       else
+           var_reloid = getrelid(var->varno, root->parse->rtable);
+
+       if (var_reloid != InvalidOid)
        {
-           item_width = get_attavgwidth(relid, var->varattno);
+           item_width = get_attavgwidth(var_reloid, var->varattno);
            if (item_width > 0)
            {
                rel->attr_widths[ndx] = item_width;