Re: Freeze avoidance of very large table.
| От | Jeff Janes |
|---|---|
| Тема | Re: Freeze avoidance of very large table. |
| Дата | |
| Msg-id | CAMkU=1xSO9v6yJH=dZopKWU7BexeJ=P_x9W-F4qwjt80U-vi+w@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Freeze avoidance of very large table. (Sawada Masahiko <sawada.mshk@gmail.com>) |
| Ответы |
Re: Freeze avoidance of very large table.
|
| Список | pgsql-hackers |
On Fri, Jul 3, 2015 at 1:25 AM, Sawada Masahiko <sawada.mshk@gmail.com> wrote:
On Fri, Jul 3, 2015 at 1:23 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On 2 July 2015 at 16:30, Sawada Masahiko <sawada.mshk@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
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