>>>> Which pg version are you using?
>>
>> I should have mentionned that before sorry: PostgreSQL 8.2
>
> I definitely would consider upgrading to 8.3 - even without any config
> changes it might bring quite some improvement.
>
> But mainly it would allow you to use "asynchronous commit" - which could
> possibly increase your throughput tremendously.
HOT can potentitally help a lot for this workload, too, if the columns
being updated are not indexed.
...Robert