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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: Robert Haas <robertmhaas(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(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: 2012-02-29 19:09:02
Message-ID: 4F4E77CE.1050101@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 29.02.2012 19:54, Simon Riggs wrote:
> I'm beginning to lose faith that objections are being raised at a
> rational level. It's not a panel game with points for clever answers,
> its an engineering debate about how to add features real users want.
> And they do want, so let me solve the problems by agreeing something
> early enough to allow it to be implemented, rather than just
> discussing it until we run out of time.

I thought my view on how this should be done was already clear, but just 
in case it isn't, let me restate: Enlarge the page header to make room 
for the checksum. To handle upgrades, put code in the backend to change 
the page format from old version to new one on-the-fly, as pages are 
read in. Because we're making the header larger, we need to ensure that 
there's room on every page. To do that, write a utility that you run on 
the cluster before running pg_upgrade, which moves tuples to ensure 
that. To ensure that the space doesn't get used again before upgrading, 
change the old version so that it reserves those N bytes in all new 
insertions and updates (I believe that approach has been discussed 
before and everyone is comfortable with backpatching such a change). All 
of this in 9.3.

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

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