Search Postgresql Archives

Re: Or selection on index versus union

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Wed, Oct 05, 2005 at 11:13:58AM +0200, han.holl@xxxxxxxxxxxxxxxxxxxx wrote:
> On Tuesday 04 October 2005 23:08, Michael Fuhr wrote:
> > On Tue, Oct 04, 2005 at 09:32:41PM +0200, han.holl@xxxxxxxxxxxxxxxxxxxx wrote:
> > > I've got a table with an index, let's call it fase.
> > >
> > > The following query is fine: 'select something from table where fase =
> > > '1';
> > >
> > > However, this is disastrously slow:
> > > select something from table where fase = '1' or fase = '2';
> >
> > Could we see some EXPLAIN ANALYZE output?  What version of PostgreSQL
> > are you using?  Have you run VACUUM ANALYZE on the table to remove
> > dead tuples and update the statistics?  Have you considered clustering
> > the table on fase's index?
> >
> 
> Oh, well, thanks. I hadn't realized that a newly loaded database needs a vacuum analyze to begin with. And what's worse, I had the impression that vacuum full would include analyze, wich I see now it doesn't.

When first loaded, there are no statistics for a table, so the database
has no idea what to expect. You don't need to vacuum a brand-new table,
but you do need to analyze it.

We've actually talked about changing the name of vacuum full so as not
to confuse people. But you really want to stay away from vacuum full
unless you have no choice, because of the exclusive lock on the table it
grabs.

> I'm not a database administrator, and I'm afraid it shows. I'm going to read a lot of docs in the coming months, because real people depend on reasonable performance of our databases.

If you need immediate help you can get commercial support from a number
of companies.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@xxxxxxxxxxxxx
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

---------------------------(end of broadcast)---------------------------
TIP 2: Don't 'kill -9' the postmaster

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Postgresql Jobs]     [Postgresql Admin]     [Postgresql Performance]     [Linux Clusters]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Books]     [PHP Databases]     [Postgresql & PHP]     [Yosemite]
  Powered by Linux