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Date: Thu, 7 Jan 2010 17:03:49 +0100
Message-ID: <852badbc1001070803y56d9bb23v83d8d35c1ecb4f33@mail.gmail.com>
Subject: Re: Air-traffic benchmark
From: Lefteris <lsidir@gmail.com>
To: Ivan Voras <ivoras@freebsd.org>
Cc: pgsql-performance@postgresql.org
Content-Type: text/plain; charset=ISO-8859-1

On Thu, Jan 7, 2010 at 4:57 PM, Ivan Voras <ivoras@freebsd.org> wrote:
> 2010/1/7 Lefteris <lsidir@gmail.com>:
>> On Thu, Jan 7, 2010 at 3:51 PM, Ivan Voras <ivoras@freebsd.org> wrote:
>>> On 7.1.2010 15:23, Lefteris wrote:
>>>
>>>> I think what you all said was very helpful and clear! The only part
>>>> that I still disagree/don't understand is the shared_buffer option:))
>>>
>>> Did you ever try increasing shared_buffers to what was suggested (around
>>> 4 GB) and see what happens (I didn't see it in your posts)?
>>
>> No I did not to that yet, mainly because I need the admin of the
>> machine to change the shmmax of the kernel and also because I have no
>> multiple queries running. Does Seq scan uses shared_buffers?
>
> Everything uses shared_buffers, even things that do not benefit from
> it. This is because shared_buffers is the part of the general database
> IO - it's unavoidable.
>


I will increase the shared_buffers once my kernel is configured and I
will report back to you.

As for the index scan, I already build an b-tree on year/month but PG
(correctly) decides not to use it. The data are from year 1999 up to
2009 (my typo mistake) so it is almost 90% of the data to be accessed.
When I ask for a specific year, like 2004 then the index is used and
query times become faster.

lefteris