From: | Michael Paquier <michael(at)paquier(dot)xyz> |
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To: | Magnus Hagander <magnus(at)hagander(dot)net> |
Cc: | Sergei Kornilov <sk(at)zsrv(dot)org>, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Offline enabling/disabling of data checksums |
Date: | 2019-03-14 00:23:42 |
Message-ID: | 20190314002342.GC3493@paquier.xyz |
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Lists: | pgsql-hackers |
On Wed, Mar 13, 2019 at 12:24:21PM +0100, Magnus Hagander wrote:
> Enabling or disabling the checksums offline on the master quite clearly
> requires a rebuild of the standby, there is no other way (this is one of
> the reasons for the online enabling in that patch, so I still hope we can
> get that done -- but not for this version).
I am curious to understand why this would require a rebuild of the
standby. Technically FPWs don't update the checksum of a page when it
is WAL-logged, so even if a primary and a standby don't agree on the
checksum configuration, it is the timing where pages are flushed in
the local instance which counts for checksum correctness.
> You mean if the backend and pg_checksums is built with different blocksize?
> Yeah, that sounds like something which is a cheap check and should be done.
Yes, we should check after that, checksum calculation uses BLCKSZ with
a hardcoded value, so a mismatch would cause computation failures. It
could be possible to not have this restriction if we made the block
size an argument of the checksum calculation though.
--
Michael
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