Re: Freeze avoidance of very large table. - Mailing list pgsql-hackers

On Tue, Nov 17, 2015 at 7:29 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
>
> On Tue, Nov 17, 2015 at 10:45 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> On Sun, Nov 15, 2015 at 1:47 AM, Amit Kapila <amit.kapila16@gmail.com>
>> wrote:
>>> On Sat, Nov 14, 2015 at 1:19 AM, Andres Freund <andres@anarazel.de>
>>> wrote:
>>>> On 2015-10-31 11:02:12 +0530, Amit Kapila wrote:
>>>> > On Thu, Oct 8, 2015 at 11:05 PM, Simon Riggs <simon@2ndquadrant.com>
>>>> > wrote:
>>>> > >
>>>> > > On 1 October 2015 at 23:30, Josh Berkus <josh@agliodbs.com> wrote:
>>>> > >>
>>>> > >> On 10/01/2015 07:43 AM, Robert Haas wrote:
>>>> > >> > On Thu, Oct 1, 2015 at 9:44 AM, Fujii Masao
>>>> > >> > <masao.fujii@gmail.com>
>>>> > wrote:
>>>> > >> >> I wonder how much it's worth renaming only the file extension
>>>> > >> >> while
>>>> > >> >> there are many places where "visibility map" and "vm" are used,
>>>> > >> >> for example, log messages, function names, variables, etc.
>>>> > >> >
>>>> > >> > I'd be inclined to keep calling it the visibility map (vm) even
>>>> > >> > if
>>>> > >> > it
>>>> > >> > also contains freeze information.
>>>> > >> >
>>>> >
>>>> > What is your main worry about changing the name of this map, is it
>>>> > about more code churn or is it about that we might introduce new
>>>> > issues
>>>> > or is it about that people are already accustomed to call this map as
>>>> > visibility map?
>>>>
>>>> Several:
>>>> * Visibility map is rather descriptive, none of the replacement terms
>>>>   imo come close. Few people will know what a 'freeze' map is.
>>>> * It increases the size of the patch considerably
>>>> * It forces tooling that knows about the layout of the database
>>>>   directory to change their tools
>>>>
>>>
>>> All these points are legitimate.
>>>
>>>> On the benfit side the only argument I've heard so far is that it allows
>>>> to disambiguate the format. But, uh, a look at the major version does
>>>> that just as well, for far less trouble.
>>>>
>>>> > It seems to me quite logical for understanding purpose as well.  Any
>>>> > new
>>>> > person who wants to work in this area or is looking into it will
>>>> > always
>>>> > wonder why this map is named as visibility map even though it contains
>>>> > information about visibility of page as well as frozen state of page.
>>>>
>>>> Being frozen is about visibility as well.
>>>>
>>>
>>> OTOH being visible doesn't mean page is frozen.  I understand that frozen
>>> is
>>> related to visibility, but still it is a separate state of page and used
>>> for
>>> different
>>> purpose.  I think this is a subjective point and we could go either way,
>>> it
>>> is
>>> just a matter in which way more people are comfortable.
>>
>> I'm stickin' with what I said before, and what I think Andres is
>> saying too: renaming the map is a horrible idea.  It produces lots of
>> code churn for no real benefit.  We usually avoid such changes, and I
>> think we should do so here, too.
>
> I understood.
> I'm going to turn the patch back to visibility map, and just add the logic
> of enhancement of VACUUM FREEZE.

Attached latest v24 patch.
I've changed patch so that just adding frozen bit into visibility map.
So the size of patch is almost half of previous one.

Please review it.

Regards,

--
Masahiko Sawada