Re: Supply restore_command to pg_rewind via CLI argument

Hi,

On Fri, Jun 18, 2021 at 5:42 PM Andrey Borodin <x4mmm@yandex-team.ru> wrote:
>
> If we run 'pg_rewind --restore-target-wal' there must be restore_command in config of target installation. But if the
configis 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.
Wesolved 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
earlierversions 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.


--
Alexey Kondratov