again on index usage - Mailing list pgsql-hackers

Hello,

I have an table with ca 1.7 million records, with the following structure:
    Table "iplog_gate200112"Attribute |   Type    | Modifier 
-----------+-----------+----------ipaddr    | inet      | input     | bigint    | output    | bigint    | router    |
text     | ipdate    | timestamp | 
 
Indices: iplog_gate200112_ipaddr_idx,        iplog_gate200112_ipdate_idx

the following query 

explain
SELECT sum(input) FROM iplog_gate200112 
WHERE  '2001-12-01 00:00:00+02' <= ipdate AND ipdate < '2001-12-02 00:00:00+02' AND  '2001-12-01 00:00:00+02' <= ipdate
ANDipdate < '2002-01-01 00:00:00+02' AND   network_subeq(ipaddr, '193.68.240.0/20') AND 'uni-gw' ~ router;
 

results in 

NOTICE:  QUERY PLAN:

Aggregate  (cost=51845.51..51845.51 rows=1 width=8) ->  Seq Scan on iplog_gate200112  (cost=0.00..51845.04 rows=190
width=8)


Why would it not want to use index scan?

Statistics for the table are as follows (from pg_statistic s, pg_attribute a, 
pg_class c
where starelid = c.oid and attrelid = c.oid and staattnum = attnum
and relname = 'iplog_gate200112')
attname | attdispersion | starelid  | staattnum | staop | stanullfrac | 
stacommonfrac |      stacommonval      |        staloval        |        
stahival
---------+---------------+-----------+-----------+-------+-------------+-------
--------+------------------------+------------------------+--------------------
----ipaddr  |   8.85397e-05 | 190565949 |         1 |  1203 |           0 |   
0.000441917 | 192.92.129.1           | 192.92.129.0           | 212.72.197.154input   |     0.0039343 | 190565949 |
   2 |   412 |           0 |     
 
0.0183278 | 0                      | 0                      | 5929816798output  |      0.724808 | 190565949 |         3
|  412 |           0 |      
 
0.835018 | 0                      | 0                      | 2639435033router  |      0.222113 | 190565949 |         4
|  664 |           0 |      
 
0.416541 | sofia5                 | bourgas1               | varna3ipdate  |      0.014311 | 190565949 |         5 |
1322|           0 |     
 
0.0580676 | 2001-12-04 00:00:00+02 | 2001-12-01 00:00:00+02 | 2001-12-31 
00:00:00+02
(5 rows)

The query 

explain
SELECT sum(input) FROM iplog_gate200112 
WHERE  ipdate < '2001-12-01 00:00:00+02'  AND  network_subeq(ipaddr, '193.68.240.0/20') AND 'uni-gw' ~ router;

produces 

Aggregate  (cost=4.91..4.91 rows=1 width=8) ->  Index Scan using iplog_gate200112_ipdate_idx on iplog_gate200112  
(cost=0.00..4.91 rows=1 width=8)

Note there are no records with ipdate < '2001-12-01 00:00:00+02' in the table.

Could anyone sched some light? This is on 7.1.3.

Daniel