Re: Another idea for index-only scans

Gregory Stark wrote:
> "Bruce Momjian" <bruce(at)momjian(dot)us> writes:
>
> > I have added another idea for index-only scans to the TODO list:
> >
> >> A third idea would be for a heap scan to check if all rows are visible
> >> and if so set a per-table flag which can be checked by index scans.
> >> Any change to the table would have to clear the flag. To detect
> >> changes during the heap scan a counter could be set at the start and
> >> checked at the end --- if it is the same, the table has not been
> >> modified --- any table change would increment the counter.
>
> I think I would prefer to address this in the same infrastructure as the
> dead-space-map. That way you're not dependent on having no updates happening
> on the table at all. Any tuples on pages which contain no in-doubt tuples
> could have their visibility check skipped but when you come across a tuple on
> a page which has been modified since the last vacuum then you have to check
> the visibility.

Yea, the bitmap/page idea is already on the TODO list. This was just a
less granular idea.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +