Yang Zhang <yanghatespam@gmail.com> writes:
> My question really boils down to: if we're interested in using COW
> snapshotting (a common feature of modern filesystems and hosting
> environments), would we necessarily need to ensure the data and
> pg_xlog are on the same snapshotted volume?
Yeah, I think so. It's possible to imagine schemes that would let
a WAL-snapshot-shortly-after-the-data-snapshot work, but you would
(at least) need to disable WAL file recycling, which there's no
provision for at the moment.
The usual approach is to use a COW snapshot only for making a base
backup of the data area, and rely on WAL streaming/archiving to copy
the WAL.
regards, tom lane