From: Chris Browne <cbbrowne@acm.org>
To: pgsql-performance@postgresql.org
Subject: Re: postgresql is slow with larger table even it is in RAM
Date: Tue, 25 Mar 2008 11:02:22 -0400
Message-ID: <603aqe979d.fsf@dba2.int.libertyrms.com> (raw)
References: <f966c2ee0803250135h57ba1d5bs41f77616ae7186dc@mail.gmail.com>
<99f1636c0803250139g321329dbr7c640213e9132583@mail.gmail.com>
<f966c2ee0803250142hae53ef4mfee4487d1fd052a2@mail.gmail.com>
sathiya.psql@gmail.com ("sathiya psql") writes:
> On Tue, Mar 25, 2008 at 2:09 PM, jose javier parra sanchez <jojapasa@gmail.com> wrote:
>
>
> It's been said zillions of times on the maillist. Using a select
> count(*) in postgres is slow, and probably will be slow for a long
> time. So that function is not a good way to measure perfomance.
>
>
>
> Yes, but if the data is in HDD then we can say this...
> but now the data is in RAM
Even if the data all is in RAM, it will still take some definitely
non-zero time to examine all of the pages, looking for tuples, and
then to determine which of those tuples are visible from the
perspective of your DB connection.
If 500MB of relevant data is sitting on disk, then it will take
whatever time it takes to pull it from disk; if it is in memory, there
is still work to be done...
--
select 'cbbrowne' || '@' || 'cbbrowne.com';
http://linuxdatabases.info/info/finances.html
Rules of the Evil Overlord #76. "If the hero runs up to my roof, I
will not run up after him and struggle with him in an attempt to push
him over the edge. I will also not engage him at the edge of a
cliff. (In the middle of a rope-bridge over a river of molten lava is
not even worth considering.)" <http://www.eviloverlord.com/;
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: cbbrowne@acm.org
Subject: Re: postgresql is slow with larger table even it is in RAM
In-Reply-To: <603aqe979d.fsf@dba2.int.libertyrms.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox