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Re: Block-level CRC checks

From: "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>
To: "Andrew Chernow" <ac(at)esilo(dot)com>
Cc: "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 14:19:01
Message-ID: 36e682920810020719g44a7dfd9of46b8fc0e233a718@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Oct 2, 2008 at 10:09 AM, Andrew Chernow <ac(at)esilo(dot)com> wrote:
> I read through this patch and am curious why 0xdeadbeef was used as an
> uninitialized value for the page crc.  Is this value somehow less likely to
> have collisons than zero (or any other arbitrary value)?

It was just an arbitrary value I chose to identify non-checksummed
pages; I believe would have the same collision rate as anything else.

> 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.

-- 
Jonah H. Harris, Senior DBA
myYearbook.com

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