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Re: Block-level CRC checks

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Greg Stark <greg(dot)stark(at)enterprisedb(dot)com>
Cc: Aidan Van Dyk <aidan(at)highrise(dot)ca>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Brian Hurt <bhurt(at)janestcapital(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2008-10-02 17:44:00
Message-ID: 20081002174400.GF4151@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg Stark escribió:

> Writing this explanation did bring to mind one solution which we had  
> already discussed for other reasons: not marking blocks dirty after hint 
> bit setting.

How about when a hint bit is set and the page is not already dirty, set
the checksum to the "always valid" value?  The problem I have with this
idea is that there would be lots of pages excluded from the CRC checks,
a non-trivial percentage of the time.

Maybe we could mix this with Simon's approach to counting hint bit
setting, and calculate a valid CRC on the page every n-th non-logged
change.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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