Weird indices

Hi,

I try to optimize our databases and I find a query that's not very
optimal :

sitefr=# explain select nomsession from session where nomsession='xxx';
NOTICE:  QUERY PLAN:

Seq Scan on session  (cost=0.00..16275.95 rows=10113 width=12)

EXPLAIN


Phew! I think there's an index missing but...

sitefr=# \d session
                             Table "session"
 Attribute  |   Type    |                    Modifier
------------+-----------+-------------------------------------------------
 idsession  | integer   | not null default nextval('seq_idsession'::text)
 nomsession | text      |
 idmembre   | text      |
 referer    | text      |
 ip         | text      |
 datelog    | timestamp |
Indices: ix_session_idmembre,
         ix_session_nomsession,
         session_idsession_key


So I look at the index itself :

sitefr=# \d ix_session_nomsession
Index "ix_session_nomsession"
 Attribute  | Type
------------+------
 nomsession | text
btree


Did I miss something or 'text' attributes (fields) can't be indexed ?
That sounds crazy ! (I vacuum analyzed many times)

Just in case 'nomsession' would not be as dispersed as I would
think...

sitefr=# select count(nomsession) from session;
 count
--------
 510069
(1 row)

sitefr=# select count(distinct nomsession) from session;
 count
--------
 401094
(1 row)

Anyone has an idea ?

Thanks !

--
Jean-Christophe Boggio
cat@thefreecat.org
Independant Consultant and Developer
Delphi, Linux, Perl, PostgreSQL