large Website – How to increase wordpress capacity?

Hi,

I have a very large number of post on my wordpress installation. More than 3,00,000 Posts are published. Most of the post i publish via cron job. Just few lines per post.

Problem is when i go beyond 3 lack, the cron jobs becomes very very slow. I have a dedicated server. I also tried this in local host. Installed on different browser. As per the developer (he is fresher), mysql is not capable of handling more pages per installation.

Fresh wordpress installation works very fast.

Any alternative?

Thanks in advance.