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(at)thefreecat(dot)org
Independant Consultant and Developer
Delphi, Linux, Perl, PostgreSQL