From: | cluster <skrald(at)amossen(dot)dk> |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Query only slow on first run |
Date: | 2007-11-27 22:51:40 |
Message-ID: | fii71p$oc1$1@news.hub.org |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-performance |
> As for optimizing the query, I noticed that all three joins are done by
> nested loops. I wonder if another join method would be faster. Have you
> analyzed all the tables?
Yes. I did a VACUUM FULL ANALYZE before running the test queries. Also I
have just performed an ANALYZE just to be sure everything was really
analyzed.
> You aren't disabling hash joins or merge joins are
> you?
Nope.
> If you aren't, then as a test I would try disabling nested loops by
> doing "set enable_nestloop=false" and see if the query is any faster for
> you.
If I disable the nested loops, the query becomes *much* slower.
A thing that strikes me is the following. As you can see I have the
constraint: q.status = 1. Only a small subset of the data set has this
status. I have an index on q.status but for some reason this is not
used. Instead the constraint are ensured with a "Filter: (q.status = 1)"
in an index scan for the primary key in the "q" table. If the small
subset having q.status = 1 could be isolated quickly using an index, I
would expect the query to perform better. I just don't know why the
planner doesn't use the index on q.status.
From | Date | Subject | |
---|---|---|---|
Next Message | Pablo Alcaraz | 2007-11-27 23:06:34 | Re: TB-sized databases |
Previous Message | Simon Riggs | 2007-11-27 20:57:25 | Re: TB-sized databases |