Re: Freeze avoidance of very large table.

On Sat, Oct 31, 2015 at 1:32 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Thu, Oct 8, 2015 at 11:05 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>
>> On 1 October 2015 at 23:30, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
>>>
>>> On 10/01/2015 07:43 AM, Robert Haas wrote:
>>> > On Thu, Oct 1, 2015 at 9:44 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)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?

My concern is mostly that I think calling it the "visibility and
freeze map" is excessively long and wordy.

One observation that someone made previously is that there is a
difference between "all-visible" and "index-only scan OK". An
all-visible page that has a HOT update is no longer all-visible (it
needs vacuuming) but an index-only scan would still be OK (because
only the non-indexed values in the tuple have changed, and every scan
scan can see either the old or the new tuple but not both. At
present, the index-only scan will consult the heap page anyway,
because all we know is that the page is not all-visible. But maybe in
the future somebody will decide to add a bit for that. Then we'd have
the "visibility, usable for index-only scans, and freeze map", but I
think "_vufiosfm" will not be a good choice for a file suffix.

So similarly here. The file suffix doesn't need to enumerate all the
bits that are present for each page.

--
Robert Haas
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