| From: | Joshua Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: increasing collapse_limits? |
| Date: | 2011-05-01 19:16:40 |
| Message-ID: | 1801535455.7112.1304277400048.JavaMail.root@mail-1.01.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Pavel,
> Actually we had to solve a issue with slow SELECT. The problem was in
> low value of JOIN_COLLAPSE_LIMITS. Can we increase a default of this
> value. I checked some complex query, and planner needed about 200ms
> for JOIN_COLLAPSE_LIMIT = 16. So some around 12 can be well.
I'm not comfortable with increasing the default, yet. While folks on dedicated good hardware can handle a collapse of 10-12 joins, a lot of people are running PostgreSQL on VMs these days whose real CPU power is no better than a Pentium IV. Also, if you're doing OLTP queries on small tables, spending 20ms planning a query is unreasonably slow in a way it is not for a DW query.
It does make a reasonable piece of advice for those tuning for DW, though. I'll add it to my list.
Speaking of which, what happened to replacing GEQO with Simulated Annealing? Where did that project go?
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com
San Francisco
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Joshua Berkus | 2011-05-01 19:18:15 | Re: Changing the continuation-line prompt in psql? |
| Previous Message | Joshua Berkus | 2011-05-01 19:10:26 | Re: branching for 9.2devel |