On Thu, Mar 27, 2025 at 5:57 PM David G. Johnston <david.g.johns...@gmail.com> wrote: > On Thu, Mar 27, 2025 at 2:28 PM Robert Treat <r...@xzilla.net> wrote: >> On Thu, Mar 27, 2025 at 12:06 PM David G. Johnston >> <david.g.johns...@gmail.com> wrote: >> > I expanded upon the material regarding using different file systems and >> > disks. >> > >> > I would like to add a similar "why" to the mount point recommendation but >> > don't know what that would be. Suggestions welcomed. >> > >> >> I'm not sure I follow what you are asking for... but a non-performance >> reason to use a seperate mount point for pg_wal, even if the >> underlying storage is the same, would be for something like using >> filesystem snapshots to grab contents of the data directory without >> grabbing wal (which can be handled separately). >> > > If I mount the filesystem on disk2 to: /mnt/disk2 > Why do I need to create "/mnt/disk2/wal_files/" and point there instead of: > "/mnt/disk2/"? >
My immediate response to this was "because Postgres won't let you" which seemed unhelpful, and that I couldn't remember why was pretty unsatisfying, so I dug around in the source which was unhelpful but eventually came across this from https://www.postgresql.org/docs/devel/creating-cluster.html#CREATING-CLUSTER-MOUNT-POINTS "Best practice is to create a directory within the mount-point directory that is owned by the PostgreSQL user, and then create the data directory within that. This avoids permissions problems,..." Which I do remember having tried to do it directly and the OS complaining that my mount point wasn't owned by root and/or Postgres complaining that the xlog dir wasn't owned by Postgres, so I think this advice probably still holds. Robert Treat https://xzilla.net
