How many posts and pages can WordPress handle?

It really mostly depends on the hardware used to host WordPress. You have to think, WordPress is used on WordPress.com which gets g-d knows how many posts a day.

Adding to that, you might review WordPress_Optimization. But the database will handle quite large sets but will your server? Might have a talk with your host, especially if you will have lots of visitors.

Thanks for responding!

I plan on using a decent dedicated server, so my main concern isn’t hardware. My concern is the appropriateness and efficiency of using WordPress for my purpose.

To be more specific. I plan on having 4 post types in one blog. They need to be queried in various ways, but the different post types don’t need to be displayed on the same page. Two post types together may total hundreds of thousands of posts, potentially millions–erring on the side of caution; and the other two post types may total hundreds of millions, potentially billions. All of them may have comments.

Is the way WordPress stores posts in the database appropriate for this task? Should I consider hacking WordPress to store some of these post types in separate databases instead? Would that significantly improve performance? Or is WordPress altogether the wrong tool for the task and I should consider looking for/developing another solution?

I think I have a solution: spreading posts over multiple blogs. This would work because a lot of my queries would be user specific, anyway. And since WordPress is advertised as being able to handle an infinite number of blogs, I imagine this would be a better way to go. There would still be one giant post type in the main blog, however.