| From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
|---|---|
| To: | Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Freeze avoidance of very large table. |
| Date: | 2015-07-08 19:31:35 |
| Message-ID: | CAMkU=1xSO9v6yJH=dZopKWU7BexeJ=P_x9W-F4qwjt80U-vi+w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Jul 3, 2015 at 1:25 AM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com>
wrote:
> On Fri, Jul 3, 2015 at 1:23 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > On 2 July 2015 at 16:30, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)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
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