Skip site navigation (1) Skip section navigation (2)

Re: Query tuning

From: Chris <dmagick(at)gmail(dot)com>
To: "Subbiah, Stalin" <SSubbiah(at)netopia(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Query tuning
Date: 2006-08-23 01:37:13
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Subbiah, Stalin wrote:
> Hello All,
> This query runs forever and ever. Nature of this table being lots of
> inserts/deletes/query, I vacuum it every half hour to keep the holes
> reusable and nightly once vacuum analyze to update the optimizer. We've
> got index on eventtime only. Running it for current day uses index range
> scan and it runs within acceptable time. Below is the explain of the
> query. Is the order by sequencenum desc prevents from applying limit
> optimization?
> explain SELECT *
> WHERE EVENTTIME>'07/23/06 16:00:00' 
> AND  EVENTTIME<'08/22/06 16:00:00' 
> AND  (OBJDOMAINID='tzRh39d0d91luNGT1weIUjLvFIcA' 
>         OR OBJID='tzRh39d0d91luNGT1weIUjLvFIcA' 
>         OR USERDOMAINID='tzRh39d0d91luNGT1weIUjLvFIcA') 
> ------------------------------------------------------------------------
> ------------------------------------------------------------------------
> ------------------------------------------------------------------------
> ------------------------------------------------------------------------
> -------------------------------------------------------------
>  Limit  (cost=15546930.29..15546931.54 rows=500 width=327)
>    ->  Sort  (cost=15546930.29..15581924.84 rows=13997819 width=327)
>          Sort Key: eventtime, sequencenum
>          ->  Seq Scan on eventlog  (cost=0.00..2332700.25 rows=13997819
> width=327)
>                Filter: ((eventtime > '2006-07-23 16:00:00'::timestamp
> without time zone) AND (eventtime < '2006-08-22 16:00:00'::timestamp
> without time zone) AND (((objdomainid)::text =
> 'tzRh39d0d91luNGT1weIUjLvFIcA'::text) OR ((objid)::text =
> 'tzRh39d0d91luNGT1weIUjLvFIcA'::text) OR ((userdomainid)::text =
> 'tzRh39d0d91luNGT1weIUjLvFIcA'::text)))
> (5 rows)
> Thanks,
> Stalin
> Pg version 8.0.1, suse 64bit.

Firstly you should update to 8.0.8 - because it's in the same stream you 
won't need to do a dump/initdb/reload like a major version change, it 
should be a simple upgrade.

Can you send explain analyze instead of just explain?

It sounds like you're not analyz'ing enough - if you're doing lots of 
updates/deletes/inserts then the statistics postgresql uses to choose 
whether to do an index scan or something else will quickly be outdated 
and so it'll have to go back to a full table scan every time..

Can you set up autovacuum to handle that for you more regularly?

Postgresql & php tutorials

In response to

pgsql-performance by date

Next:From: Tom LaneDate: 2006-08-23 02:34:59
Subject: Re: Moving a tablespace
Previous:From: Michael FuhrDate: 2006-08-23 01:36:08
Subject: Re: Moving a tablespace

Privacy Policy | About PostgreSQL
Copyright © 1996-2017 The PostgreSQL Global Development Group