Re: Freeze avoidance of very large table.

On Fri, Mar 11, 2016 at 6:16 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Mar 10, 2016 at 1:41 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> On Fri, Mar 11, 2016 at 1:03 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>>> This 001 patch looks so little like what I was expecting that I
>>> decided to start over from scratch. The new version I wrote is
>>> attached here. I don't understand why your version tinkers with the
>>> logic for setting the all-frozen bit; I thought that what I already
>>> committed dealt with that already, and in any case, your version
>>> doesn't even compile against latest sources. Your version also leaves
>>> the scan_all terminology intact even though it's not accurate any
>>> more, and I am not very convinced that the updates to the
>>> page-skipping logic are actually correct. Please have a look over
>>> this version and see what you think.
>>
>> Thank you for your advise.
>> Sorry, optimising logic of previous patch was old by mistake.
>> Attached latest patch incorporated your suggestions with a little revising.
>
> Thanks. I adopted some of your suggested, rejected others, fixed a
> few minor things that I missed previously, and committed this. If you
> think any of the changes that I rejected still have merit, please
> resubmit those changes as separate patches.
>

Thank you for your effort to this feature and committing it.
I guess that I couldn't do good work to this feature at final stage,
but I really appreciate all your advice and suggestion.

> I think what I really want is some logic so that if we have a 1-page
> visibility map in the old cluster and the second half of that page is
> all zeroes, we only create a 1-page visibility map in the new cluster
> rather than a 2-page visibility map.
>
> Or more generally, if the old VM is N pages, but the last half of the
> last page is empty, then let the output VM be 2*N-1 pages instead of
> 2*N pages.
>

I got your point.
Attached latest patch can skip to write the last part of last old page
if it's empty.
Please review it.

Regards,

--
Masahiko Sawada