Re: Remove Deprecated Exclusive Backup Mode - Mailing list pgsql-hackers
| From | Magnus Hagander |
|---|---|
| Subject | Re: Remove Deprecated Exclusive Backup Mode |
| Date | |
| Msg-id | CABUevEzS8Q-mOcfRaNmux88G6tmtFA1isVfw4wb4_HSHWuj+QQ@mail.gmail.com Whole thread Raw |
| In response to | Re: Remove Deprecated Exclusive Backup Mode (Jehan-Guillaume de Rorthais <jgdr@dalibo.com>) |
| Responses |
Re: Remove Deprecated Exclusive Backup Mode
Re: Remove Deprecated Exclusive Backup Mode |
| List | pgsql-hackers |
On Thu, Jul 2, 2020 at 1:06 AM Jehan-Guillaume de Rorthais <jgdr@dalibo.com> wrote:
On Wed, 1 Jul 2020 15:58:57 -0400
Robert Haas <robertmhaas@gmail.com> wrote:
> On Wed, Jul 1, 2020 at 3:50 PM Magnus Hagander <magnus@hagander.net> wrote:
> > As far as I've seen, the one thing that people have problems with in the
> > exclusive mode backups are precisely the fact that they have to keep a
> > persistent conneciton open, and thus it cannot work together with backup
> > software that is limited to only supporting running a pre- and a post
> > script.
> >
> > Something like I have suggested here is to solve *that* problem. I don't
> > think anybody actually explicitly wants "exclusive backups" -- they want a
> > backup solution that plugs into their world of pre/post scripts. And if we
> > can make that one work in a safer way than the current exclusive backups,
> > ohw is that not an improvement?
>
> Yeah, I guess that's a pretty fair point. I have to confess to having
> somewhat limited enthusiasm for adding a third mode here, but it might
> be worth it.
>
> It seems pretty well inevitable to me that people are going to forget
> to end them.
There's so many way an admin could break their backup process and not notice
it. Even with current nonexclusive backup, a bad written script might creates
bad unrecoverable backups.
Definitely. And the scariest part of them is that they all work fine in testing...
In regard with your concern, monitoring in progress backups might be *one*
answer, from server side. This was "easy" with exclusive backup, we just
monitor the backup_label age and warn if it is older than expected [1]. Using
Yeah, but having a monitoring point that will crash your database on restart isn't very safe :)
non-exclusive backup...this is not that easy anymore. And pg_is_in_backup() is
quite misleading if the admin found it without reading doc. Maybe an admin
Yeah, as it is now it should really be called pg_is_in_exclusive_backup().
function to list in progress non-exclusive backup and related backend pid might
be a good start?
I think it would make perfect sense to show manual (exclusive or non-exclusive) base backups in pg_stat_progress_basebackup. There's no fundamental need that one should only be for base backups taken with pg_basebackup. In fact, I'd argue that's a mistake in the view in v13 that it does not include this information.
It could have "phase" set to "manual non-exclusive" for example, and leave the other fields at NULL.
I guess in theory even for exclusive ones, with the pid column set to NULL. (As Stephen mentioned at some point in the future we might also want to extend it to allow these tools to report their progress as well into it, probably by just calling an admin function on the connection that they already have).
Tools like pg_basebackup (and probably pgbackrest/barman to some extends) still
need the backup to abort on disconnection. Maybe it could flag its session
using the replication protocol or call a new admin function or load a hook on
session-shutdown to keep previous API behavior?
Suddenly requiring a replication protocol connection for one thing, when all their other things are done over a normal one, seems really terrible. But having an admin function would work.
But anything requiring loading of a hook is going to raise the bar massively as suddenly somebody needs to install a compiled binary on the server in order to use it. But calling a separate function is pretty much what I suggested upthread (except I suggested a new version of pg_stop_backup, but implementation wise)
But I'm not sure what previous API behavior you're looking to preserve here?
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