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* How to determine if my setting for shared_buffers is too high?
@ 2006-12-07 16:42 Bill Moran <wmoran@collaborativefusion.com>
2006-12-07 17:04 ` Re: How to determine if my setting for shared_buffers is too high? Tom Lane <tgl@sss.pgh.pa.us>
2006-12-08 19:19 ` Re: How to determine if my setting for shared_buffers is too high? Jim C. Nasby <jim@nasby.net>
0 siblings, 2 replies; 3+ messages in thread
From: Bill Moran @ 2006-12-07 16:42 UTC (permalink / raw)
To: pgsql-performance
I'm gearing up to do some serious investigation into performance for
PostgreSQL with regard to our application. I have two issues that I've
questions about, and I'll address them in two seperate emails.
This one regards tuning shared_buffers.
I believe I have a good way to monitor database activity and tell when
a database grows large enough that it would benefit from more
shared_buffers: if I monitor the blks_read column of pg_stat_database,
it should increase very slowly if there is enough shared_buffer
space. When shared buffer space runs out, more disk read requests
will be required and this number will begin to climb.
If anyone sees a flaw in this approach, I'd be interested to hear it.
The other tuning issue with shared_buffers is how to tell if I'm
allocating too much. For example, if I allocate 1G of RAM to
shared buffers, and the entire database can fit in 100M, that 900M
might be better used as work_mem, or something else.
I haven't been able to find anything regarding how much of the
shared buffer space PostgreSQL is actually using, as opposed to
simply allocating.
--
Bill Moran
Collaborative Fusion Inc.
wmoran@collaborativefusion.com
Phone: 412-422-3463x4023
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: How to determine if my setting for shared_buffers is too high?
2006-12-07 16:42 How to determine if my setting for shared_buffers is too high? Bill Moran <wmoran@collaborativefusion.com>
@ 2006-12-07 17:04 ` Tom Lane <tgl@sss.pgh.pa.us>
1 sibling, 0 replies; 3+ messages in thread
From: Tom Lane @ 2006-12-07 17:04 UTC (permalink / raw)
To: Bill Moran <wmoran@collaborativefusion.com>; +Cc: pgsql-performance
Bill Moran <wmoran@collaborativefusion.com> writes:
> I haven't been able to find anything regarding how much of the
> shared buffer space PostgreSQL is actually using, as opposed to
> simply allocating.
In 8.1 and up, contrib/pg_buffercache/ would give you some visibility
of this.
regards, tom lane
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: How to determine if my setting for shared_buffers is too high?
2006-12-07 16:42 How to determine if my setting for shared_buffers is too high? Bill Moran <wmoran@collaborativefusion.com>
@ 2006-12-08 19:19 ` Jim C. Nasby <jim@nasby.net>
1 sibling, 0 replies; 3+ messages in thread
From: Jim C. Nasby @ 2006-12-08 19:19 UTC (permalink / raw)
To: Bill Moran <wmoran@collaborativefusion.com>; +Cc: pgsql-performance
Remember that as you increase shared_buffers you might need to make the
bgwriter more aggressive too.
On Thu, Dec 07, 2006 at 11:42:39AM -0500, Bill Moran wrote:
>
> I'm gearing up to do some serious investigation into performance for
> PostgreSQL with regard to our application. I have two issues that I've
> questions about, and I'll address them in two seperate emails.
>
> This one regards tuning shared_buffers.
>
> I believe I have a good way to monitor database activity and tell when
> a database grows large enough that it would benefit from more
> shared_buffers: if I monitor the blks_read column of pg_stat_database,
> it should increase very slowly if there is enough shared_buffer
> space. When shared buffer space runs out, more disk read requests
> will be required and this number will begin to climb.
>
> If anyone sees a flaw in this approach, I'd be interested to hear it.
>
> The other tuning issue with shared_buffers is how to tell if I'm
> allocating too much. For example, if I allocate 1G of RAM to
> shared buffers, and the entire database can fit in 100M, that 900M
> might be better used as work_mem, or something else.
>
> I haven't been able to find anything regarding how much of the
> shared buffer space PostgreSQL is actually using, as opposed to
> simply allocating.
>
> --
> Bill Moran
> Collaborative Fusion Inc.
>
> wmoran@collaborativefusion.com
> Phone: 412-422-3463x4023
>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
>
--
Jim Nasby jim@nasby.net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
^ permalink raw reply [nested|flat] 3+ messages in thread
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2006-12-07 16:42 How to determine if my setting for shared_buffers is too high? Bill Moran <wmoran@collaborativefusion.com>
2006-12-07 17:04 ` Tom Lane <tgl@sss.pgh.pa.us>
2006-12-08 19:19 ` Jim C. Nasby <jim@nasby.net>
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