Re: Patroni, slots, and expiring WALs

On 2023-03-28 17:08:38 +0200, Alexander Kukushkin wrote:
> On Tue, 28 Mar 2023 at 16:55, Peter J. Holzer <hjp-pgsql(at)hjp(dot)at> wrote:
>
>
> However, when we took down one node for about two hours for some tests
> recently (with some moderate traffic on the remaining node), the replica
> didn't catch up after being restarted and inspection of the logs showed
> that it was trying to get WALs which had already been deleted.
>
>
>
> It is impossible to know whether it is down temporarily or gone forever,
> therefore the slot is removed as soon as the member key expires (after TTL).
>  

TTL is 30 seconds by default. So that doesn't seem very useful.

> So apparently, `use_slots: true` isn't enough. What else do I have to
> configure? (I know about wal_keep_size, but it was my understanding that
> this isn't needed when slots are used)
>
>
> The best option is to configure continuous archiving and PITR. Backups are
> always important.

Yeah, but for the given application a daily dump is sufficient for
backups, so I'd like to keep that simple.

> The second option - you can put all member names into permanent slots
> configuration (using patronictl edit-config):
> slots:
>   nodename1:
>     type: physical
>   nodename2:
>     type: physical
>   nodename3:
>     type: physical
>
> This way slots representing these members will not be removed.

That seems to work (at least the slot didn't disappear within a few
minutes). I'll do some more testing.

hp

--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | hjp(at)hjp(dot)at | -- Charles Stross, "Creative writing
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