Re: [Patch] pg_rewind: options to use restore_command from recovery.conf or command line

From: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
To: Alexey Kondratov <a(dot)kondratov(at)postgrespro(dot)ru>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, vladimirlesk(at)yandex-team(dot)ru, Dmitriy Sarafannikov <dsarafan(at)yandex-team(dot)ru>
Subject: Re: [Patch] pg_rewind: options to use restore_command from recovery.conf or command line
Date: 2018-10-22 10:11:25
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Hi, Alexey!

> 19 окт. 2018 г., в 22:49, Alexey Kondratov <a(dot)kondratov(at)postgrespro(dot)ru> написал(а):
> I expect, that it will be a good idea to allow pg_rewind to look for a restore_command
Normally you do not expect huge progress on failed master. But you still can get a lot of WAL if you have network partition and scheduled tasks like pg_repack.
I'm not actually aware what kind of problems led to these but we were considering some automation to fetch WALs for failed master to improve rewinded\resetuped ratio.
> I prepared a proof of concept patch (please, find attached), which does exactly what I described above. I played with it a little and it seems to be working, tests were accordingly updated to verify this archive retrieval functionality too.
> Patch is relatively simple excepting the one part: if we want to parse recovery.conf (with all possible includes, etc.) and get restore_command, then we should use guc-file.l parser, which is heavily linked to backend, e.g. in error reporting part. So I copied it and made frontend-safe version guc-file-fe.l. Personally, I don't think it's a good idea, but nothing else came to mind. It is also possible to leave the only one option -- passing restore_command as command line argument.
I think it is better to load restore_command from recovery.conf.

I didn't actually try patch yet, but the idea seems interesting. Will you add it to the commitfest?

Best regards, Andrey Borodin.

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