> Greg Smith <gsm...@gregsmith.com> writes: >> Yesterday Jignesh Shah presented his extensive benchmark results >> comparing >> 8.4-beta1 with 8.3.7 at PGCon: >> http://blogs.sun.com/jkshah/entry/pgcon_2009_performance_comparison_of > >> While most cases were dead even or a modest improvement, his dbt-2 >> results >> suggest a 15-20% regression in 8.4. Changing the >> default_statistics_taget >> to 100 was responsible for about 80% of that regression. The remainder >> was from the constraint_exclusion change. That 80/20 proportion was >> mentioned in the talk but not in the slides. Putting both those back to >> the 8.3 defaults swapped things where 8.4b1 was ahead by 5% instead. > > Yeah, I saw that talk and I'm concerned too, but I think it's premature > to conclude that the problem is precisely that stats_target is now too > high. I'd like to see Jignesh check through the individual queries in > the test and make sure that none of them had plans that changed for the > worse. The stats change might have just coincidentally tickled some > other planning issue.
Wouldn't he just need to rerun the tests with default_stats_target set to the old value? I presume he has actually done this already in order to come to the conclusion he did about the cause of the regression. cheers andrew -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
