"Dave Dutcher" <dave@xxxxxxxxxxxx> writes: > Thanks for looking into it. I thought I might actually test if it was the > patch you mentioned which changed my results, but I haven't had time. > Because you mentioned it was grouping on the results of a UNION ALL which > was throwing off the row estimate I changed my query from a UNION ALL/GROUP > BY to a GROUP BY/FULL OUTER JOIN. The view runs a hair slower by itself, > but the better estimate of rows makes it work much better for joining with. I took another look and think I found the problem: 8.2's new code for flattening UNION ALL subqueries into "append relations" is failing to initialize all the fields of the appendrel, which confuses estimate_num_groups (and perhaps other places). I think this will fix it for you. regards, tom lane Index: allpaths.c =================================================================== RCS file: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v retrieving revision 1.154 diff -c -r1.154 allpaths.c *** allpaths.c 4 Oct 2006 00:29:53 -0000 1.154 --- allpaths.c 28 Jan 2007 18:44:01 -0000 *************** *** 384,389 **** --- 384,395 ---- } /* + * Set "raw tuples" count equal to "rows" for the appendrel; needed + * because some places assume rel->tuples is valid for any baserel. + */ + rel->tuples = rel->rows; + + /* * Finally, build Append path and install it as the only access path for * the parent rel. (Note: this is correct even if we have zero or one * live subpath due to constraint exclusion.)
