Re: avoid multiple hard links to same WAL file after a crash

On Mon, May 02, 2022 at 07:48:18PM +0900, Michael Paquier wrote:
> Skimming through at the buildfarm logs, it happens that the tests are
> able to see this race from time to time. Here is one such example on
> rorqual:
> https://buildfarm.postgresql.org/cgi-bin/show_stage_log.pl?nm=rorqual&dt=2022-04-20%2004%3A47%3A58&stg=recovery-check
>
> And here are the relevant logs:
> 2022-04-20 05:04:19.028 UTC [3109048][startup][:0] LOG: restored log
> file "00000002.history" from archive
> 2022-04-20 05:04:19.029 UTC [3109111][walreceiver][:0] LOG: fetching
> timeline history file for timeline 2 from primary server
> 2022-04-20 05:04:19.048 UTC [3109111][walreceiver][:0] FATAL: could
> not link file "pg_wal/xlogtemp.3109111" to "pg_wal/00000002.history":
> File exists
> [...]
> 2022-04-20 05:04:19.234 UTC [3109250][walreceiver][:0] LOG: started
> streaming WAL from primary at 0/3000000 on timeline 2
>
> The WAL receiver upgrades the ERROR to a FATAL, and restarts
> streaming shortly after. Using durable_rename() would not be an issue
> here.

Thanks for investigating this one. I think I agree that we should simply
switch to durable_rename() (without a file existence check beforehand).

--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com