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Re: PITR Backups

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
Cc: "Dan Gorman" <dgorman(at)hi5(dot)com>, "Toru SHIMOGAKI" <shimogaki(dot)toru(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-performance(at)postgresql(dot)org
Subject: Re: PITR Backups
Date: 2007-06-22 18:02:44
Message-ID: 24724.1182535364@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
"Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> On Fri, 2007-06-22 at 13:12 -0400, Tom Lane wrote:
>> If you saw a problem I'd be inclined to question whether
>> there is some upstream component (OS or disk controller) that's
>> reordering writes.

> Given thats exactly what they do, constantly, I don't think its safe to
> say that it works since we cannot verify whether that has happened or
> not.

If he's trying to snapshot at a level of hardware that's behind a
write-caching disk controller, I agree that that's untrustworthy.

If not, ie if he's snapshotting the actual durable state of the storage
system, then any problems in the snapshot indicate a problem with the
database's ability to recover from a crash.  So I don't think you should
tell him to not worry.

			regards, tom lane

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