On Fri, May 31, 2013 at 11:00:19AM -0700, Josh Berkus wrote: > Bruce, > > > Roberts statement was: > > > >> Loss or corruption of a single visibility map page means possible loss > >> of half a gigabyte of data. > > I fail to be alarmed at this; currently losing a single page of the clog > causes just as widespread corruption (worse, actually, since it's not > confined to one table). It does point to the eventual need to checksum > these things, though. > > > Certainly unidentified corruption of a visibility map page could easily > > cause incorrect results. So, technically, _adding_ bits would cause > > corruption. > > Yes, that's already true. I'm pointing out that if we depend on the > vismap for all-frozen, then losing bits *also* causes corruption, so > that's something we need to test for. Right now, there is no possible > corruption from losing bits; we simply end up scannning more pages than > we have to.
Right, and it is hard to see that losing and adding are somehow more/less likely, so it seems we already realy on the visibility map being correct. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
