Re: possible TODO: read-only tables, select from indexes only.

On Sat, 23 Apr 2005 03:14 am, Bruce Momjian wrote:
> Hannu Krosing wrote:
> > On R, 2005-04-22 at 11:40 -0400, Bruce Momjian wrote:
> > > See this TODO:
> > >  
> > >  * Allow data to be pulled directly from indexes
> > >  
> > >    Currently indexes do not have enough tuple visibility information
> > >    to allow data to be pulled from the index without also accessing
> > >    the heap.  One way to allow this is to set a bit to index tuples
> > >    to indicate if a tuple is currently visible to all transactions
> > >    when the first valid heap lookup happens. 
> > 
Storing visibility information in the index has always been put down as a cause of
performance problems.  Would it be plausible to have an index type that included the
information and one that didn't.  You could choose which way you wanted to go.

I know especially for some tables, I would choose this index with visibility as it would
increase performance by not looking at the table at all for that information (count being a good example).  However
for general purpose indexes I would use the normal index with no visibility information.

The possibly of the bit method or full tuples is probably a decision for others, but having
the flexibility to choose in this would be a great thing.

Regards

Russell Smith