| 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 |
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| 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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