How many files do search engines index per directory

I'm using Apache Mod RewriteRule to deal with dynamic URLs. And trying to figure out the best URL structure to go with.

Here are the opt开发者_StackOverflowions I am thinking about:

They will all rewrite to: mydomain.com/myprogram.php?username=$1&cat=$2&item=$3

Option 1: mydomain.com/username-category-item-5.html

Option 2: mydomain.com/username/category-item-5.html

Option 3: mydomain.com/username/category/item-5.html

My concern is with how the search engines will crawl and index the pages. If I use option 1 all users files will appear to be in the same directory. Will this make the search engines index only a limited number of the pages?

And if I go with option 2 or 3 what is a safe number of sub directories to use when optimizing for search engines?

Go with the last. It's clearer all around, not even counting what search engines think of it.

May I suggest you simply use:

http://mydomain.com/username/category/item

Ensure that all of your links are "Reachable". I was recently involved in a site with this type of structure. The problem was, the Search Engines did not know about all of the links. So we added a page per user, which linked to each category page, which listed links to all the items.

Traffic doubled within 3 months.