Postgresql simple query performance question

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

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