| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> |
| Cc: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, jd(at)commandprompt(dot)com, Steve Crawford <scrawford(at)pinpointresearch(dot)com>, pgsql-performance(at)postgresql(dot)org, Ben Chobot <bench(at)silentmedia(dot)com> |
| Subject: | Re: BBU Cache vs. spindles |
| Date: | 2010-10-21 16:59:46 |
| Message-ID: | 201010211659.o9LGxkV01781@momjian.us |
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| Lists: | pgsql-performance pgsql-www |
Kevin Grittner wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
> > With a BBU you can turn off full_page_writes
>
> My understanding is that that is not without risk. What happens if
> the WAL is written, there is a commit, but the data page has not yet
> been written to the controller? Don't we still have a torn page?
I don't see how full_page_writes affect non-written pages to the
controller.
full_page_writes is designed to guard against a partial write to a
device. I don't think the raid cache can be partially written to, and
the cache will not be cleared until the drive has fully writen the data
to disk.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
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