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Re: Block-level CRC checks

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>
Cc: "Brian Hurt" <bhurt(at)janestcapital(dot)com>, "Aidan Van Dyk" <aidan(at)highrise(dot)ca>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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 13:42:23
Message-ID: 87y717glkw.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-hackers
"Jonah H. Harris" <jonah(dot)harris(at)gmail(dot)com> writes:

> On Thu, Oct 2, 2008 at 9:07 AM, Brian Hurt <bhurt(at)janestcapital(dot)com> wrote:
>> I have a stupid question wrt hint bits and CRC checksums- it seems to me
>> that it should be possible, if you change the hint bits, to be able to very
>> easily calculate what the change in the CRC checksum should be.
>
> Doesn't the problem still remain?  The problem being that the buffer
> can be changed as it's written, yes?

It's even worse than that. Two processes can both be fiddling hint bits on
different tuples (or even the same tuple) at the same time.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's RemoteDBA services!

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