I am not sure whether PostgreSQL depends on system call `fsyncdata` to
sync data to disk. If yes, then I don't think it's safe to use NFS.
When `fsyncdata` returns success, it doesn't mean the data has
really been synced to disk. But if PostgreSQL crashes right after
it returns success to clients. Eventually it breaks the D (Durability) of
ACID.
Benjamin
"Peter J. Holzer" <hjp-pgsql@hjp.at> writes:
> On 2025-07-14 10:07:20 -0400, Tom Lane wrote:
>> That is primarily for safety reasons: if for some reason the
>> filesystem gets dismounted, or hasn't come on-line yet during
>> a reboot, you do not want Postgres to be able to write on the
>> underlying mount-point directory.
> Be careful: There are two different directorys involved in a mount
> point. The one in the parent filesystem and the one in the mounted file
> system.
True, and the safety requirement really is only that the parent
filesystem's mount-point directory not be writable by us.
But normal practice is that both directories are root-owned,
or at least owned by highly privileged users.
(I have a vague idea that there are system-level security hazards,
not specific to Postgres, if mount-point directories are publicly
writable. Don't feel like researching that though.)
regards, tom lane
