On Wed, Jan 25, 2017 at 7:37 PM, Andres Freund <and...@anarazel.de> wrote: > On 2017-01-25 19:30:08 -0500, Stephen Frost wrote: >> * 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? >> >> 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. > > Uh. Writes aren't atomic on that granularity. That means you very well > *can* see a torn page (in linux you can e.g. on 4KB os page boundaries > of a 8KB postgres page). Just read a page while it's being written out.
Yeah. This is also why backups force full page writes on even if they're turned off in general. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
