[GENERAL] posgres tunning

I have a drupal site working with postgres that does not tolerate more than 200 concurrent connections(it is not hardware fault). Does anybody know how to adjust postgres parameters and what are them?, or how to get a better performance in any way?

[GENERAL] 2 instance of postgres service running against same db files?

Can I have 2 instance of postgres service running against same db???. I meant 2 machine or the same machine with a 2 running executing postgres process (if it is in the same machine, then through different ports), working with the same db files, may be in a shared storage or any common mounted f