From: | Michael Stone <mstone+postgres(at)mathom(dot)us> |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Mostly read performance |
Date: | 2005-08-12 00:30:31 |
Message-ID: | 20050812003031.GP19080@mathom.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-performance |
On Thu, Aug 11, 2005 at 07:13:27PM -0400, Jeffrey Tenny wrote:
>The system for testing was 512MB
That's definately *not* a "large ram" system. If you're reading a subset
of data that totals 70MB I'm going to guess that your data set is larger
than or at least a large fraction of 512MB.
>additional memory. However there was no swap activity on that system,
>so I doubt memory was the limiting factor.
The system won't swap if your data set is larger than your memory, it
just won't cache the data.
>Well, that's what you'd expect. But a first time 70MB fetch on a
>freshly rebooted system took just as long as all secondary times. (Took
>over a minute to fetch, which is too long for my needs, at least on
>secondary attempts).
If the query involves a table scan and the data set is larger than your
available memory, you'll need a full scan every time. If you do a table
scan and the table fits in RAM, subsequent runs should be faster. If you
have an index and only need to look at a subset of the table, subsequent
runs should be faster. Without knowing more about your queries it's not
clear what your situation is.
Mike Stone
From | Date | Subject | |
---|---|---|---|
Next Message | Petr Kavan | 2005-08-12 06:53:33 | How many views is ok? |
Previous Message | Michael Stone | 2005-08-11 23:54:44 | Re: PG8 Tuning |