On Fri, Apr 24, 2015 at 1:31 AM, Jim Nasby <Jim.Nasby@bluetreble.com> wrote:
> On 4/23/15 11:06 AM, Petr Jelinek wrote:
>>
>> On 23/04/15 17:45, Bruce Momjian wrote:
>>>
>>> On Thu, Apr 23, 2015 at 09:45:38AM -0400, Robert Haas wrote:
>>> Agreed, no extra file, and the same write volume as currently. It would
>>> also match pg_clog, which uses two bits per transaction --- maybe we can
>>> reuse some of that code.
>>>
>>
>> Yeah, this approach seems promising. We probably can't reuse code from
>> clog because the usage pattern is different (key for clog is xid, while
>> for visibility/freeze map ctid is used). But visibility map storage
>> layer is pretty simple so it should be easy to extend it for this use.
>
>
> Actually, there may be some bit manipulation functions we could reuse;
> things like efficiently counting how many things in a byte are set. Probably
> doesn't make sense to fully refactor it, but at least CLOG is a good source
> for cut/paste/whack.
>
I agree with adding a bit that indicates corresponding page is
all-frozen into VM, just like CLOG.
I'll change the patch as second version patch.
Regards,
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Sawada Masahiko