Re: Occasional giant spikes in CPU load

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Craig James <craig_james(at)emolecules(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, David Rees <drees76(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Occasional giant spikes in CPU load
Date: 2010-04-14 21:58:33
Message-ID: 201004142158.o3ELwXL09621@momjian.us
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Craig James wrote:
> On 4/7/10 5:47 PM, Robert Haas wrote:
> > On Wed, Apr 7, 2010 at 6:56 PM, David Rees<drees76(at)gmail(dot)com> wrote:
> >>> max_fsm_pages = 16000000
> >>> max_fsm_relations = 625000
> >>> synchronous_commit = off
> >>
> >> You are playing with fire here. You should never turn this off unless
> >> you do not care if your data becomes irrecoverably corrupted.
> >
> > That is not correct. Turning off synchronous_commit is sensible if
> > you don't mind losing the last few transactions on a crash. What will
> > corrupt your database is if you turn off fsync.
>
> A bit off the original topic, but ...
>
> I set it this way because I was advised that with a battery-backed
> RAID controller, this was a safe setting. Is that not the case?

To get good performance, you can either get a battery-backed RAID
controller or risk losing a few transaction with synchronous_commit =
off. If you already have a battery-backed RAID controller, there is
little benefit to turning synchronous_commit off, and some major
downsides (possible data loss).

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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