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Re: Block-level CRC checks

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>
Cc: Andrew Chernow <ac(at)esilo(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Gregory Stark <stark(at)enterprisedb(dot)com>, pgsql(at)mohawksoft(dot)com, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, "Decibel!" <decibel(at)decibel(dot)org>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2008-10-02 14:27:15
Message-ID: 48E4DA43.7020703@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Jonah H. Harris wrote:
> On Thu, Oct 2, 2008 at 10:09 AM, Andrew Chernow <ac(at)esilo(dot)com> wrote:
>> Would it not be better to add a boolean bit or byte to inidcate the crc
>> state?
> 
> Ideally, though we don't have any spare bits to play with in MAXALIGN=4.

In the page header? There's plenty of free bits in pd_flags.

But isn't it a bit dangerous to have a single flag on the page 
indicating whether the CRC is valid or not? Any corruption that flips 
that bit would make the CRC check to be skipped.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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