* Robert Haas (robertmh...@gmail.com) wrote: > On Wed, Jan 25, 2017 at 7:19 PM, Michael Paquier > <michael.paqu...@gmail.com> wrote: > > On Thu, Jan 26, 2017 at 9:14 AM, Peter Geoghegan <p...@heroku.com> wrote: > >> On Wed, Jan 25, 2017 at 3:30 PM, Stephen Frost <sfr...@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? > > > > Why? What do you foresee here? I would think such backup solutions are > > careful enough to ensure correctly the durability of pages so as they > > are not partially written. > > Well, you'd have to keep a read(fd, buf, 8192) performed by the backup > tool from overlapping with a write(fd, buf, 8192) performed by the > backend.
As Michael mentioned, that'd depend on if things are atomic from a user's perspective at certain sizes (perhaps 4k, which wouldn't be too surprising, but may also be system-dependent), in which case verifying that the page is in the WAL would be sufficient. Thanks! Stephen
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