On Wed, Apr 18, 2018 at 12:35 AM, Michael Paquier <michael@paquier.xyz> wrote:
That looks like a rather difficult problem to solve in PostgreSQL itself, as the operator running the cluster is in charge of setting up the FS options which would control the COW behavior, so it seems to me
You cannot turn off CoW on ZFS. What other behavior would you refer to here?
I suppose one could make a dedicated data set for the WAL and have ZFS make a reservation for about 2x the total expected WAL size. It would require careful attention to detail if you increase WAL segments configuration, though, and if you had any kind of hiccup with streaming replication that caused the segments to stick around longer than expected (but that's no different from any other file system).