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Re: PITR Backups

From: Dan Gorman <dgorman(at)hi5(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Simon Riggs" <simon(at)2ndquadrant(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: 2007-06-25 15:26:52
Message-ID: 0099C2EC-E872-44E3-BA0A-64D58DFDFE5F@hi5.com (view raw or flat)
Thread:
Lists: pgsql-performance
It's the latter, is snapshot of the durable state of the storage  
system (e.g. it will never be corrupted)

Regards,
Dan Gorman

On Jun 22, 2007, at 11:02 AM, Tom Lane wrote:

> "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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