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Re: 16-bit page checksums for 9.2

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Dan Scales <scales(at)vmware(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, david(at)fetter(dot)org, aidan(at)highrise(dot)ca, stark(at)mit(dot)edu, pgsql-hackers(at)postgresql(dot)org
Subject: Re: 16-bit page checksums for 9.2
Date: 2012-01-28 20:44:32
Message-ID: 4F245E30.20704@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 28.01.2012 15:49, Simon Riggs wrote:
> On Fri, Jan 27, 2012 at 9:07 PM, Dan Scales<scales(at)vmware(dot)com>  wrote:
>
>> Also, I missed this before:  don't you want to add the checksum calculation (PageSetVerificationInfo) to mdextend() (or preferably smgrextend()) as well?  Otherwise, you won't be checksumming a bunch of the new pages.
>
> You don't need to checksum the extend because no data is written at
> that point.

That's not correct. smgrextend writes a block of data just like 
smgrwrite does. When a relation is extended by the buffer manager, it 
calls smgrextend with an all-zeros block, but not all callers do that. 
See rewriteheap.c and nbtsort.c for counter-examples.

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

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