Re: Proposal: Another attempt at vacuum improvements

On Thu, May 26, 2011 at 4:10 PM, Pavan Deolasee
<pavan(dot)deolasee(at)gmail(dot)com> wrote:
> On Thu, May 26, 2011 at 9:40 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
>> Currently, I believe the only way a page can get marked all-visible is
>> by vacuum.  But if we make this change, then it would be possible for
>> a HOT cleanup to encounter a situation where all-visible could be set.
>>  We probably want to make that work.
>>
>
> Yes. Thats certainly an option.
>

BTW, I just realized that this design would expect the visibility map
to be always correct or at least it should always correctly report a
page having dead line pointers. We would expect the index vacuum to
clean index pointers to *all* dead line pointers because once the
index vacuum is complete, other backends or next heap vacuum may
remove any of those old dead line pointers assuming that index vacuum
would have taken care of the index pointers.

IOW, the visibility map bit must always be clear when there are dead
line pointers on the page. Do we guarantee that today ? I think we do,
but the comment in the source file is not affirmative.

Thanks,
Pavan

--
Pavan Deolasee
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