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Re: Block-level CRC checks

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2009-12-01 13:08:18
Message-ID: 1259672898.13774.13164.camel@ebony (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, 2009-12-01 at 07:58 -0500, Bruce Momjian wrote:
> bruce wrote:
> > What might be interesting is to report CRC mismatches if the database
> > was shut down cleanly previously;  I think in those cases we shouldn't
> > have torn pages.
> 
> Sorry, stupid idea on my part.  We don't WAL log hit bit changes so
> there is no guarantee the page is in WAL on recovery.

I thought it was a reasonable idea. We would need to re-check CRCs after
a crash and zero any that mismatched. Then we can start checking them
again as we run.

In any case, it seems strange to do nothing to protect the database in
normal running just because there is one type of problem that occurs
when we crash.

-- 
 Simon Riggs           www.2ndQuadrant.com


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