Bruce,

> 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.

Seems marginal at best.  Checking overlap between the index and the FSM/DSM 
and only check dirty pages seems more intelligent, and able to cover a 
larger number of cases.

-- 
--Josh

Josh Berkus
PostgreSQL @ Sun
San Francisco

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