On Fri, 2009-05-22 at 16:43 +0000, Greg Sabino Mullane wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: RIPEMD160 > > > > 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 situation where the stats target being so low hurts things the most > > are the data warehouse use cases.
Nor is it our primary user base. If we want to do this we need to have more than one conf as a tmpl. > > That doesn't seem to be reality here though, and it's questionable whether > > this change really helps the people who need to fool with the value the > > most. > > The goal of defaults is not to help people who fool with the value - it's to > get a good default out of the box for people who *don't* fool with all the > values. :) Right. If someone is really doing a DW they are already spending time with the postgresql.conf. > > But unless someone has some compelling evidence to the contrary, it looks > > like > > the stats target needs to go back to a lower value. > > Please don't. This is a very good change, and I don't see why changing it back > because it might hurt people doing DW is a good thing, when most of users are > not doing DW. I haven't seen any evidence to suggest that Jignesh's findings provide anything but a single data point in a vast metric of our smallest user base. Reverting a value based on that seems like a mistake. > > > As for the change to constraint_exclusion, the regression impact there is > > much less severe and the downside of getting it wrong is pretty bad. > > Similarly, the people who are affected by something like presumably are not > running a default postgresql.conf anyway, so they can toggle it back to > squeeze > a little more performance out of their system. > Right. Joshua D. Drake -- PostgreSQL - XMPP: jdr...@jabber.postgresql.org Consulting, Development, Support, Training 503-667-4564 - http://www.commandprompt.com/ The PostgreSQL Company, serving since 1997 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
