From: | Jaime Casanova <jcasanov(at)systemguards(dot)com(dot)ec> |
---|---|
To: | Jim Nasby <decibel(at)decibel(dot)org> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Smith <greg(at)2ndquadrant(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: shared_buffers documentation |
Date: | 2010-04-20 19:45:19 |
Message-ID: | l2u3073cc9b1004201245ie6f4f7dak53cc7ba9b1f54e4f@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, Apr 20, 2010 at 12:07 PM, Jim Nasby <decibel(at)decibel(dot)org> wrote:
> On Apr 16, 2010, at 4:56 PM, Robert Haas wrote:
>> From reading this and other threads, I think I generally understand
>> that the perils of setting shared_buffers too high: memory is needed
>> for other things, like work_mem, a problem which is exacerbated by the
>> fact that there is some double buffering going on. Also, if the
>> buffer cache gets too large, checkpoints can involve writing out
>> enormous amounts of dirty data, which can be bad.
>
> I've also seen large shared buffer settings perform poorly outside of IO issues, presumably due to some kind of internal lock
> contention. I tried running 8.3 with 24G for a while, but dropped it back down to our default of 8G after noticing some performance
> problems. Unfortunately I don't remember the exact details, let alone having a repeatable test case.
>
i have heard this before, sadly enough i don't have a machine for that
kind of tests and can't use my customer's production servers for such
things :) so, i always set shared buffers lower than 8Gb even if i
have ram for more...
someone can confirm the lock contention theory? this should be
noticeable at checkpoint time right?
--
Atentamente,
Jaime Casanova
Soporte y capacitación de PostgreSQL
Asesoría y desarrollo de sistemas
Guayaquil - Ecuador
Cel. +59387171157
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