Re: Index usage vs large repetitions of key

On Tue, 7 May 2002, Neil Conway wrote:

> On Tue, 7 May 2002 09:48:13 -0400 (EDT)
> "Francisco Reyes" <lists@natserv.com> wrote:
> > On Sun, 5 May 2002 felix@crowfix.com wrote:
> > > I think there is some way to force an indexed read, but I have
> > > forgotten what little I knew about that.  If there is, you could try
> > > both ways and compare timings.
> >
> > Based on this info it may make sense to let it do the sequential scan.
>
> You can easily test this hypothesis by disabling sequential scans (SET
> enable_seqscan = off;), and using EXPLAIN ANALYZE to compare the performance
> of the resulting query plan with the one chosen by the planner to
> begin with.

I tried to set enable_seqscan = off and it still did a sequential scan.

> > Is there a drawback on having the index right now?
>
> Yes; inserts and updates will need to update the index. Depending on
> your queries, this can be a significant performance hit.


This is a "reporting" server and I do a set of "copy" jobs once a day,
followed by a vacuum analyze.. and a nightly "vacuum full"