| From: | "Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM> |
|---|---|
| To: | "'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | RE: CRCs |
| Date: | 2001-01-12 23:14:50 |
| Message-ID: | 8F4C99C66D04D4118F580090272A7A234D327A@sectorbase1.sectorbase.com |
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| Lists: | pgsql-hackers |
> > It wouldn't help you recover, but you would be able to report that
> > you cannot recover.
>
> How? The scenario Vadim is pointing out is where the disk
> drive writes a changed data block in advance of the WAL log entry
> describing the change. Then power drops and the WAL entry never gets
> made. At restart, how will you realize that that data block now
> contains data you don't want? There's not even a log entry telling
> you you need to look at it, much less one that tells you what should
> be in it.
>
> AFAICS, disk-block CRCs do not guard against mishaps involving intended
> writes. They will help guard against data corruption that might creep
> in due to outside factors, however.
I couldn't describe better -:)
Vadim
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