Anyone know of a free, quick, or theoretical way to test out a LAMP config as to how many visitors it could handle? Is there formula?

Currently I have a Linode 80, Debian Sarge, Apache2, PHP4, Mysql4

1 Joomla site
1 PHPSurveyor
1 DotProject

You can try something liike JMeter to load test with varying levels of users.

I don't think a formula is possible since the number of possible users will depend on the resources usage of your php stuff and what latency is acceptable.

I have not tried this but have been meaning to:

http://httpd.apache.org/test/flood/

You can also benchmark your MySQL performance, with a couple of tools as mentioned in the MySQL manual: http://dev.mysql.com/doc/refman/5.0/en/ ... marks.html

Haven't checked myself yet, but I plan to fairly soon.

It all depends on really:

• How efficient your PHP code is
• How well your queries perform (right indices in the tables etc)
• How many queries each page will potentially do

...and stuff like that.

If your PHP is tight and doesn't make too many SQL queries in rapid succession, you should be able to support quite a large number of users simultaneously. I suppose it does depend on what you're going to run - I haven't seen the apps you mention, so I couldn't comment.

Just remember that there is a finite I/O limit on everything - if you use PHP to access MySQL, you're going to open a minimum of 3-5 file descriptors (maybe more if you are accessing many different tables in those queries)

If you start talking in the 1,000s of users range, creating 3,000-5,000 I/O descriptors, performance will begin to lag.

The best way is to try out tools like Flood and MySQL super-smack (be warned - that thing can bring your server to its knees very, very quickly) and see if you can't tune it for better performance.

Hope this helps,
Pete

(edited for formatting of list)