Jeff Davis <pg...@j-davis.com> writes: > On Thu, 2010-03-18 at 16:50 -0400, Tom Lane wrote: >> The VM is (a) not compressed and (b) not correctness-critical. >> Wrong bit values don't do any serious damage.
> The VM cause wrong results if a bit is set that's not supposed to be -- > right? Am I missing something? How does a seq scan skip visibility > checks and still produce right results, if it doesn't rely on the bit? It doesn't. The only thing we currently rely on the VM for is deciding whether a page needs vacuuming --- and even that we don't trust it for when doing anti-wraparound vacuuming. The worst-case consequence of a wrong bit is failure to free some dead tuples until the vacuum freeze limit expires. In order to do things like not visiting a page during scans, we'll have to solve the reliability issues. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers