* Peter Geoghegan (pg@heroku.com) wrote:
> On Wed, Jan 25, 2017 at 3:30 PM, Stephen Frost <sfrost@snowman.net> wrote:
> > As it is, there are backup solutions which *do* check the checksum when
> > backing up PG. This is no longer, thankfully, some hypothetical thing,
> > but something which really exists and will hopefully keep users from
> > losing data.
>
> Wouldn't that have issues with torn pages?
No, why would it? The page has either been written out by PG to the OS,
in which case the backup s/w will see the new page, or it hasn't been.
Our testing has not turned up any issues as yet. That said, it's
relatively new and I wouldn't be surprised if we need to do some
adjustments in that area, which might be system-dependent even. We
could certainly check the WAL for the page that had a checksum error (we
currently simply report them, though don't throw away a prior backup if
we detect one).
This isn't like a case where only half the page made it to the disk
because of a system failure though; everything is online and working
properly during an online backup.
Thanks!
Stephen