> Hi,
>
> Bruce Momjian:
> > >
> > > test=# explain select id from bench1 order by id;
> > > Sort (cost=38259.21..38259.21 rows=300000 width=4)
> > > -> Seq Scan on bench1 (cost=0.00..6093.00 rows=300000 width=4)
> > >
> > The heap is unordered, meaning a sequential scan and order by is usually
> > faster than an index walk unless there is a restrictive WHERE clause.
> >
> What heap? The index is a b-tree in this case. Thus you should be able
> to walk it and get the sorted result without ever touching the data
> file.
>
> Whether that makes sense with the current structure of the PostgreSQL
> backend is a different question, of course. Certain othr databases
> (no, not just MySQL ;-) are capable of doing that optimization, however.
We can't read data from the index. It would be nice if we could, but we
can't. I think we believe that there are very few cases where this
would be win. Usually you need non-indexed data too.
-- Bruce Momjian | http://www.op.net/~candle pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
