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Re: Block-level CRC checks

From: Florian Weimer <fweimer(at)bfk(dot)de>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2008-10-01 16:04:06
Message-ID: 82d4ik8fpl.fsf@mid.bfk.de (view raw or flat)
Thread:
Lists: pgsql-hackers
* Heikki Linnakangas:

> Currently, hint bit updates are not WAL-logged, and thus no full page
> write is done when only hint bits are changed. Imagine what happens if
> hint bits are updated on a page, but there's no other changes, and we
> crash so that only one half of the new page version makes it to disk
> (= torn page). The CRC would not match, even though the page is
> actually valid.

The non-logged hint bit writes are somewhat dangerous anyway.  Maybe
it's time to get rid of this peculiarity, despite the performance
impact?

-- 
Florian Weimer                <fweimer(at)bfk(dot)de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstra├če 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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