Re: tuning questions - Mailing list pgsql-performance

From Andrew Sullivan
Subject Re: tuning questions
Date
Msg-id 20031204181152.GO6080@libertyrms.info
Whole thread Raw
In response to Re: tuning questions  (Dror Matalon <dror@zapatec.com>)
Responses Re: tuning questions  (Eric Soroos <eric-psql@soroos.net>)
List pgsql-performance
On Thu, Dec 04, 2003 at 09:57:38AM -0800, Dror Matalon wrote:
>
> I've seen this comment several times from different people.
> Would someone care to explain how you would get data corruption? I
> thought that the whole idea of the log is to provide a journal similar
> to what you get in a journaling file system.

> So what am I missing in this picture?

That a journalling file system can _also_ have file corruption if you
have write caching enabled and no battery back up.  If the drive
tells the OS, "Yep!  It's all on the disk!" bit it is _not_ actually
scribed in the little bitty magnetic patterns -- and at that very
moment, the power goes away -- the data that was reported to have been
on the disk, but which was actually _not_ on the disk, is no longer
anywhere.  (Well, except in the past.  But time travel was disabled
some versions ago. ;-)

A

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Andrew Sullivan                         204-4141 Yonge Street
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<andrew@libertyrms.info>                              M2P 2A8
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