Re: Offline enabling/disabling of data checksums

From: Andres Freund <andres(at)anarazel(dot)de>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: Michael Banck <michael(dot)banck(at)credativ(dot)de>, Postgres hackers <pgsql-hackers(at)postgresql(dot)org>, Michael Paquier <michael(at)paquier(dot)xyz>
Subject: Re: Offline enabling/disabling of data checksums
Date: 2019-02-03 10:21:09
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On 2019-01-09 07:07:17 +0100, Fabien COELHO wrote:
> There is still no documentation.

Michael, are you planning to address this? It'd also be useful to state
when you just don't agree with things / don't plan to address them.

Given the docs piece hasn't been addressed, and seems uncontroversial,
I'm marking this patch as returned with feedback. Please resubmit once

> > > Also, the full page is rewritten... would it make sense to only overwrite
> > > the checksum part itself?
> >
> > So just writing the page header? I find that a bit scary and don't
> > expect much speedup as the OS would write the whole block anyway I
> > guess? I haven't touched that yet.
> Possibly the OS would write its block size, which is not necessary the same
> as postgres page size?

I think it'd be a bad idea to write more granular. Very commonly that'll
turn a write operation into a read-modify-write (although caching will
often prevent that from being a problem here), and it'll be bad for
flash translation layers.


Andres Freund

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