On Fri, Jul 3, 2015 at 1:25 AM, Sawada Masahiko <sawada.m...@gmail.com> wrote:
> On Fri, Jul 3, 2015 at 1:23 AM, Simon Riggs <si...@2ndquadrant.com> wrote: > > On 2 July 2015 at 16:30, Sawada Masahiko <sawada.m...@gmail.com> wrote: > > > >> > >> Also, the flags of each heap page header might be set PD_ALL_FROZEN, > >> as well as all-visible > > > > > > Is it possible to have VM bits set to frozen but not visible? > > > > The description makes those two states sound independent of each other. > > > > Are they? Or not? Do we test for an impossible state? > > > > It's impossible to have VM bits set to frozen but not visible. > These bit are controlled independently. But eventually, when > all-frozen bit is set, all-visible is also set. > If that combination is currently impossible, could it be used indicate that the page is all empty? Having a crash-proof bitmap of all-empty pages would make vacuum truncation scans much more efficient. Cheers, Jeff
