I had seen a post by Wordpress where they mention that they support unlimited 'tags' (as opposed to categories). Since php is driving Wordpress, would you mind explaining how/why they can make such a statement?
Suppose I create a wordpress site with thousands of posts and let's say 100,000 tags. Can you explain in php/mysql terms why retrieving posts for a tag on a shared hosting site (hostgator), can work?
Bonus points if you can explain why it won't work for Wordpress categories
Edit: Here is the support article on wordpress.com - http://en.support.wordpress.com/posts/categories-vs-tags/
and the statement:
Is there a limit to the number of tags I can have? Yes, the sky. In other words, no.
Edit 2: What I am really looking if some insight into the php/sql server process which might make scalability possible or not. I am not looking for using hardware to scale the system or for solutions like clustering or enhancing the database in anyway.
I am interested in things like: "querying a table with 100K entries can be quite responsive with php/mysql on a shared host" or if you think not "these queries will not work after 100k entries in the posts table"