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Re: Enabling Checksums

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Florian Pflug <fgp@phlo.org>
Cc: Ants Aasma <ants@cybertec.at>, Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@2ndquadrant.com>, Jeff Davis <pgsql@j-davis.com>, Heikki Linnakangas <hlinnakangas@vmware.com>, Simon Riggs <simon@2ndquadrant.com>, Greg Smith <greg@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2013-04-17T16:42:51Z
Lists: pgsql-hackers 
On Wed, Apr 17, 2013 at 06:33:58PM +0200, Florian Pflug wrote:
> > I was going to ask about the flexibility of pg_upgrade and checksums. 
> > Right now you have to match the old and new cluster checksum modes, but
> > it seems it would be possible to allow pg_upgrade use from checksum to
> > no-checksum servers.  Does the backend look at the pg_controldata setting,
> > or at the page checksum flag?  If the former, it seems pg_upgrade could
> > run a a no-checksum server just fine that had checksum information on
> > its pages.  This might give us more flexibility in changing the checksum
> > algorithm in the future, i.e. you only lose checksum ability.
> 
> AFAIK, there's currently no per-page checksum flag. Still, being only
> able to go from checksummed to not-checksummed probably is for all
> practical purposes the same as not being able to pg_upgrade at all.
> Otherwise, why would people have enabled checksums in the first place?

Good point, but it is _an_ option, at least.

I would like to know the answer of how an upgrade from checksum to
no-checksum would behave so I can modify pg_upgrade to allow it.


-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +