Postgresql simple query performance question - Mailing list pgsql-general

Hi
We are in the process of testing for migration of our database from Oracle to Postgresql.
I hava a simple query

Select count(*) from foo
This table has 29384048 rows and is indexed on foo_id

The tables are vacuumed and the explain plan for postgresql is

QUERY PLAN                                                                                   

------------------------------------------
 Aggregate  (cost=1194020.60..1194020.61 rows=1 width=0) (actual time=68797.280..68797.280 rows=1 loops=1)                               
   ->  Seq Scan on foo  (cost=0.00..1120560.48 rows=29384048 width=0) (actual
time=0.232..60657.948 rows=29384048 loops=1)
 Total runtime: 68797.358 ms                                                                 
                                       

The explain plan for oracle is
                    
OPERATION            OBJECT                    ACCESS_PREDICATES     FILTER_PREDICATES    
 -------------------  ------------------------  --------------------  --------------------
 SELECT STATEMENT ()  (null)                    (null)                (null)               
  SORT (AGGREGATE)    (null)                    (null)                (null)               
   INDEX (FULL SCAN)  foo_IDX_ID  (null)        (null)   

Oracle uses index for count(*) query in this case
This query in   Oracle takes only 5 sec and in postgresql it takes 1 min 10sec          

The same query in oracle without the index and full table scan(like in postgresql) has the

explain plan like this and it takes 34 sec.

select /*+ full(foo1) */ count(*) from foo1

OPERATION                OBJECT              ACCESS_PREDICATES     FILTER_PREDICATES    
 -----------------------  ------------------  --------------------  --------------------
 SELECT STATEMENT ()      (null)              (null)                (null)               
  SORT (AGGREGATE)        (null)              (null)                (null)   
    TABLE ACCESS (FULL)   foo                 (null)                (null)


In short the query "Select count(*) from foo" takes the following time:
Postgresql - 1m 10 sec
Oracle(index scan) - 5 sec
Oracle (full table scan) - 34 sec

How can I speed up this query in postgresql ? The other postgres settings are

postgresql    
        
   max_connections = 100
   shared_buffers = 50000                 
   temp_buffers = 5000
   work_mem = 16384                         
   maintenance_work_mem = 262144  
   fsync = on                             
   wal_sync_method = fsync
   effective_cache_size = 300000   
   random_page_cost =      4               
   cpu_tuple_cost = 0.01               
   cpu_index_tuple_cost = 0.001         
   cpu_operator_cost = 0.0025  

Are there any tuning that need to be done in the OS  or database side? I had attached the iostat and vmstat results of postgresql

Thanks