Re: could not link file in wal restore lines

On Fri, Jul 22, 2022 at 04:24:54AM -0500, Zsolt Ero wrote:
> I've opened an issue on pgbackrest, where the developer confirmed that
> those files are not touched by pgbackrest, they are basically copied back
> exactly as they were. The backup/restore is on the same partition as the
> data folder, so no chance of file system changes, etc. Single master, no
> replication.
>
> I'm always doing clean data dir + init_db so there is nothing there before
> the restore. I can replicate this behaviour 100%.
>
> PostgreSQL version: psql (PostgreSQL) 12.11 (Ubuntu 12.11-1.pgdg18.04+1)
>
> OS is Ubuntu 18.04
>
> pgbackrest issue: https://github.com/pgbackrest/pgbackrest/issues/1815
>
> log details:
>
> could not link file "pg_wal/000000010000015600000098" to
> "pg_wal/00000001000001570000006E": File exists

FWIW, the backend code has protections to prevent *exactly* this kind
of problems when recycling WAL segment files at checkpoints with a set
of LWLocks taken on the control file, for one.  Perhaps you have
messed up things and you have finished in such a state that backrest
writes to pg_wal/ concurrently with a cluster running and running a
checkpoint, which would explain those link() calls to be failing?
--
Michael