Re: Supply restore_command to pg_rewind via CLI argument

On Fri, Jun 18, 2021 at 10:06 PM Alexey Kondratov
<kondratov(dot)aleksey(at)gmail(dot)com> wrote:
> On Fri, Jun 18, 2021 at 5:42 PM Andrey Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
> >
> > If we run 'pg_rewind --restore-target-wal' there must be restore_command in config of target installation. But if the config is not within $PGDATA\postgresql.conf pg_rewind cannot use it.
> > If we run postmaster with `-c config_file=/etc/postgresql/10/data/postgresql.conf`, we simply cannot use the feature. We solved the problem by putting config into PGDATA only during pg_rewind, but this does not seem like a very robust solution.
> >
>
> Yeah, Michael was against it, while we had no good arguments, so
> Alexander removed it, IIRC. This example sounds reasonable to me. I
> also recall some complaints from PostgresPro support folks, that it is
> sad to not have a cli option to pass restore_command. However, I just
> thought about another recent feature --- ensure clean shutdown, which
> is turned on by default. So you usually run Postgres with one config,
> but pg_rewind may start it with another, although in single-user mode.
> Is it fine for you?
>
> >
> > Maybe we could add "-C, --target-restore-command=COMMAND target WAL restore_command\n" as was proposed within earlier versions of the patch[0]? Or instruct pg_rewind to pass config to 'postgres -C restore_command' run?
>
> Hm, adding --target-restore-command is the simplest way, sure, but
> forwarding something like '-c config_file=...' to postgres sounds
> interesting too. Could it have any use case beside providing a
> restore_command? I cannot imagine anything right now, but if any
> exist, then it could be a more universal approach.
>
> >
> > From my POV adding --target-restore-command is simplest way, I can extract corresponding portions from original patch.
> >
>
> I will have a look, maybe I even already have this patch separately. I
> remember that we were considering adding this option to PostgresPro,
> when we did a backport of this feature.
>

Here it is. I have slightly adapted the previous patch to the recent
pg_rewind changes. In this version -C does not conflict with -c, it
just overrides it.

--
Alexey Kondratov