Re: More Performance

> 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)
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