Re: Freeze avoidance of very large table.

On Fri, Apr 24, 2015 at 11:21 AM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> wrote:
> On Fri, Apr 24, 2015 at 1:31 AM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)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.
>

The second patch is attached.

In second patch, I added a bit that indicates all tuples in page are
completely frozen into visibility map.
The visibility map became a bitmap with two bit per heap page:
all-visible and all-frozen.
The logics around vacuum, insert/update/delete heap are almost same as
previous version.

This patch lack some point: documentation, comment in source code,
etc, so it's WIP patch yet,
but I think that it's enough to discuss about this.

Please feedbacks.

Regards,

-------
Sawada Masahiko