Re: Add recovery to pg_control and remove backup_label

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Postgres hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Add recovery to pg_control and remove backup_label
Date: 2023-11-20 23:52:08
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On Mon, Nov 20, 2023 at 12:37:46PM -0800, Andres Freund wrote:
> Given that, I wonder if what we should do is to just add a new field to
> pg_control that says "error out if backup_label does not exist", that we set
> when creating a streaming base backup

That would mean that one still needs to take an extra step to update a
control file with this byte set, which is something you had a concern
with in terms of compatibility when it comes to external backup
solutions because more steps are necessary to take a backup, no? I
don't quite see why it is different than what's proposed on this
thread, except that you don't need to write one file to the data
folder to store the backup label fields, but two, meaning that there's
a risk for more mistakes because a clean backup process would require
more steps.

With the current position of the fields in ControlFileData, there are
three free bytes after backupEndRequired, so it is possible to add
that for free. Now, would you actually need an extra field knowing
that backupStartPoint is around?

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