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Re: Block-level CRC checks

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Brian Hurt <bhurt(at)janestcapital(dot)com>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2008-10-02 13:50:07
Message-ID: 48E4D18F.90808@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Brian Hurt wrote:
> Jonah H. Harris wrote:
>> 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?
>>
> Another possibility is to just not checksum the hint bits...

That would work. But I'm afraid it'd make the implementation a lot more 
invasive, and also slower. The buffer manager would have to know what 
kind of a page it's dealing with, heap or index or FSM or what, to know 
where the hint bits are. Then it would have to follow the line pointers 
to locate the hint bits, and mask them out for the CRC calculation.

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

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Subject: Re: Interval output bug in HAVE_INT64_TIMESTAMP
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