From: Michael Stone <mstone+postgres@mathom.us>
To: pgsql-performance@postgresql.org
Subject: Re: Specifications for a new server
Date: Tue, 13 May 2014 10:19:13 -0400
Message-ID: <9f5e8e56-daa8-11e3-aa78-00163eeb5320@msgid.mathom.us> (raw)
In-Reply-To: <CAGZ55DQAT+Wa0ziFc9B9ArOuRGZq0qn07N4p7F_KpgnrhgYBPA@mail.gmail.com>
References: <CAGZ55DQ+7Mf0=dyohDYF5KjoovU_K+RjjPP-VaUMx9Dd92H4Mg@mail.gmail.com>
<20140506110714.GA9155@mathom.us>
<CAGZ55DQAT+Wa0ziFc9B9ArOuRGZq0qn07N4p7F_KpgnrhgYBPA@mail.gmail.com>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
On Thu, May 08, 2014 at 10:11:38AM +0200, Johann Spies wrote:
>I understand your remark about the CPU in the light of my wrong assumption
>earlier, but I do not understand your remark about the RAM. The fact that
>temporary files of up to 250Gb are created at times during complex queries, is
>to me an indication of too low RAM.
If you can afford infinite RAM, then infinite RAM is great. If your
working set size exceeds the memory size, then you will eventually need
to deal with disk IO. At that point, maybe a bit more memory will help
and maybe it will not--you'll be able to fit a little bit more working
data into memory, but that won't likely radically change the
performance. (If you can afford to fit *everything* you need into RAM
than that's ideal, but that's not the case for most people with
non-trival data sets.) What is certain is that improving the disk IO
performance will improve your overall performance if you're IO bound.
(And the mere existence of temporary files isn't an indication of
insufficient RAM if the system can utilize the memory more efficiently
with the files than it can without them--they could contain data that
isn't needed in a particular phase of a query, freeing up resources that
are needed for other data in that phase.)
Mike Stone
--
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance
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: mstone+postgres@mathom.us
Subject: Re: Specifications for a new server
In-Reply-To: <9f5e8e56-daa8-11e3-aa78-00163eeb5320@msgid.mathom.us>
* 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