On Sun, Jan 23, 2005 at 06:45:36PM -0300, Alvaro Herrera wrote:
> On Sun, Jan 23, 2005 at 03:19:10PM -0600, Jim C. Nasby wrote:
>
> > > People have this weird notion that an index-based plan is always faster
> > > than anything else. If you like you can try the operation with "set
> > > enable_seqscan = off", but I bet it will take longer.
> >
> > Well, every other database I've used can do index covering, which means
> > index scans *are* faster.
>
> ... on those database systems. Indexes are different in Postgres in
> general: they don't have visibility info (other systems don't need it,
> tuples are always visible), and in some databases you have clustered
> indexes, where the index is also the heap.
Yes, I understand. I was just pointing out that in other databases, an
index scan of even the entire table can be faster, hence the mentality
that index scans are always better.
I really hope that the current discussion on hackers about tuple
visibility in indexes leads somewhere; I think that would be a huge gain
for PostgreSQL.
--
Jim C. Nasby, Database Consultant decibel@xxxxxxxxxxx
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