Slow website queries Please Help Me

I need help, I have been dealing with this issues for over a month now and don’t know any way around it.

My wordpress install has about 50,000 posts on the website. Recently with more and more website traffic I haver one SQL query that is taking nearly all my CPU speed and causing the server to crash.

What does this nasty little query do?
SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts INNER JOIN wp_term_relationships ON (wp_posts.

Is there some way I can get rid of this query or at least limit it to not run forever?

I am currently using W3 caching plugin but it does not help. Also the wp_term_relationships database show about 70,000 entries.

Does anyone have the answer to this problem?