Re: Another idea for index-only scans

Jeff Davis wrote:
> On Wed, 2007-08-15 at 11:54 -0400, Bruce Momjian wrote:
> > 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.
> 
> This sounds useful for read-only or read-mostly tables.

I think it's too coarse-grained to be really useful.  If it was one bit
per page it could work, but one bit per relation is going to be reset
too frequently.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support