On Fri, Oct 14, 2022 at 02:15:19PM +0530, Bharath Rupireddy wrote: > Given that temp file name includes WAL file name, epoch to > milliseconds scale and MyProcPid, can there be name collisions after a > server crash or even when multiple servers with different pids are > archiving/copying the same WAL file to the same directory?
While unlikely, I think it's theoretically possible. If there is a collision, archiving should fail and retry later with a different temporary file name. > What happens to the left-over temp files after a server crash? Will > they be lying around in the archive directory? I understand that we > can't remove such files because we can't distinguish left-over files > from a crash and the temp files that another server is in the process > of copying. The temporary files are not automatically removed after a crash. The documentation for basic archive has a note about this [0]. > If the goal is to copy files atomically, why can't we name the temp > file 'wal_file_name.pid.temp', assuming no PID wraparound and get rid > of appending time? Since basic_archive is a test module illustrating > archive_library implementation, do we really need to worry about name > collisions? Yeah, it's debatable how much we care about this for basic_archive. We previously decided that we at least care a little [1], so that's why we have such elaborate temporary file names. If anything, I hope that the presence of this logic causes archive module authors to think about these problems. > The patch LGTM. Thanks! [0] https://www.postgresql.org/docs/devel/basic-archive.html#id-1.11.7.15.6 [1] https://postgr.es/m/CA%2BTgmoaSkSmo22SwJaV%2BycNPoGpxe0JV%3DTcTbh4ip8Cwjr0ULQ%40mail.gmail.com -- Nathan Bossart Amazon Web Services: https://aws.amazon.com
