RE: Re: Dissapearing indexes, what's that all about?

What are the costs associated with the EXPLAIN output? Perhaps a sequential scan is *faster* then an index scan.

Mike Mascari
mascarm(at)mascari(dot)com

-----Original Message-----
From: Daniel ?erud [SMTP:zilch(at)home(dot)se]
Sent: Sunday, April 01, 2001 12:31 PM
To: pgsql-general(at)postgresql(dot)org
Subject: Re: Re: [GENERAL] Dissapearing indexes, what's that all about?

> >Hey people,
> >have a very strange problem now...
> >It's that when my database with the script i'm using a
> >explain select * from acc where username='britta' yields
an
> >index scan. Very nice. But after some time being up the
> >same thing yields a SEQUENTIAL scan. What's happening
> >folks? =) No more than update's select's and vacuums has
> >been invoked.
>
> Are you doing vacuum or vacuum analyze? I believe only
the 'vacuum analyze'
> function cleans up the indexing statistics.
>
> len
>

Please look at this:
I just ran an interesting little test here...
watch this:

<DROP DB><CREATE DB><RUN DB SCRIPT>

explain select * from acc where username='britta';

Index scan using acc_username_key on acc...

VACUUM;

explain select * from acc where username='britta';

Seq Scan on acc

<DROP DB><CREATE DB><RUN DB SCRIPT>

explain select * from acc where username='britta';

Index scan

VACUUM ANALYZE

explain select * from acc where username='britta';

Seq scan

What the wakk is goin on here people? =)

version: PostgreSQL 7.0.0 on i686-pc-linux-gnu, compiled by
gcc 2.95.2

Thanks

Daniel Akerud

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