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From: Stephen Frost <[email protected]>
To: Andres Freund <[email protected]>
Cc: David Christensen <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: Peter Geoghegan <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: [PATCHES] Post-special page storage TDE support
Date: Wed, 8 Nov 2023 09:04:13 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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	<[email protected]>

Greetings,

* Andres Freund ([email protected]) wrote:
> On 2023-05-09 17:08:26 -0500, David Christensen wrote:
> > From 965309ea3517fa734c4bc89c144e2031cdf6c0c3 Mon Sep 17 00:00:00 2001
> > From: David Christensen <[email protected]>
> > Date: Tue, 9 May 2023 16:56:15 -0500
> > Subject: [PATCH v4 1/3] Add reserved_page_space to Page structure
> >
> > This space is reserved for extended data on the Page structure which will be ultimately used for
> > encrypted data, extended checksums, and potentially other things.  This data appears at the end of
> > the Page, after any `pd_special` area, and will be calculated at runtime based on specific
> > ControlFile features.
> >
> > No effort is made to ensure this is backwards-compatible with existing clusters for `pg_upgrade`, as
> > we will require logical replication to move data into a cluster with
> > different settings here.
> 
> The first part of the last paragraph makes it sound like pg_upgrade won't be
> supported across this commit, rather than just between different settings...
> 
> I think as a whole this is not an insane idea. A few comments:

Thanks for all the feedback!

> - Why is it worth sacrificing space on every page to indicate which features
>   were enabled?  I think there'd need to be some convincing reasons for
>   introducing such overhead.

In conversations with folks (my memory specifically is a discussion with
Peter G, added to CC, and my apologies to Peter if I'm misremembering)
there was a pretty strong push that a page should be able to 'stand
alone' and not depend on something else (eg: pg_control, or whatever) to
provide info needed be able to interpret the page.  For my part, I don't
have a particularly strong feeling on that, but that's what lead to this
design.

Getting a consensus on if that's a requirement or not would definitely
be really helpful.

Thanks,

Stephen


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