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                      
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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