Re: Concurrency issue in pg_rewind

> 18 сент. 2020 г., в 11:59, Michael Paquier <michael(at)paquier(dot)xyz> написал(а):
>
> On Fri, Sep 18, 2020 at 11:31:26AM +0500, Andrey M. Borodin wrote:
>> This is whole point of having prefetch. restore_command just links
>> file from the same partition.
>
> If this stuff is willing to do so, you may have your reasons, but even
> if you wish to locate both pg_wal/ and the prefetch path in the same
> partition, I don't get why it is necessary to have the prefetch path
> included directly in pg_wal? You could just use different paths for
> both. Say, with a base partition at /my/path/, you can just have
> /my/path/pg_wal/ that the Postgres backend links to, and
> /my/path/wal-g/prefetch/ for the secondary path.

This complexity doesn't seem necessary to me. What we gain? Prefetched WAL is WAL per se. Makes sense to keep it in pg_wal tree by default.

I will implement possibility to move cache out of pg_wal (similar functionality is implemented in pgBackRest). But it seems useless to me: user can configure WAL prefetch to be less performant, without any benefits.

Best regards, Andrey Borodin.