| From: | Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at> |
|---|---|
| To: | "'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | "Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | AW: CRCs (was Re: [GENERAL] Re: Loading optimization) |
| Date: | 2001-01-12 09:29:20 |
| Message-ID: | 11C1E6749A55D411A9670001FA6879633681AF@sdexcsrv1.f000.d0188.sd.spardat.at |
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| Lists: | pgsql-hackers |
> A disk-block CRC would detect partially written blocks (ie, power drops
> after disk has written M of the N sectors in a block). The disk's own
> checks will NOT consider this condition a failure.
But physical log recovery will rewrite every page that was changed
after last checkpoint, thus this is not an issue anymore.
> I'm not convinced
> that WAL will reliably detect it either (Vadim?). Certainly WAL will
> not help for corruption caused by external agents, away from any updates
> that are actually being performed/logged.
The external agent (if malvolent) could write a correct CRC anyway.
If on the other hand the agent writes complete garbage, vacuum will notice.
Andreas
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