Can someone explain to me, how could i know how much server resources is required to execute some php script, i mean how demanding is that script? Without that i'm never sure which way of coding is better than any other. Is there any site where i can test it or some kind of software?

Thanks,
Milan

Not really... At least, not that easily...

What you are looking to is a profiler. PHP have a really good one existing.
Xdebug:
http://www.xdebug.org
The thing is that Xdebug must be installed on the server, as it's an extension of PHP, and if you use a shared server, you won't be able to install it.

But, couple it with wincachegrind ( windows: http://sourceforge.net/projects/wincachegrind) or Kcachegrind (linux: http://kcachegrind.sourceforge.net/cgi-bin/show.cgi ), and it will show you how much time is spend in which functions, and how many time those functions where called.



But what it shows you, is which share of the total run time was needed for a specific function, not how many pressure was put on the server.
For that, there is only 1 way as I know of: a load test.
Pratically, you send bots to your site, that will makes a lot of requests to emulate several user browsing your site at the same time, and you keep a server resources monitoring opened, to see how many requests/seconds uses how many resources.

This is especially true with services like apache, who are threaded, and for which you cannot know before you run which one correspond to each process.

Thank you very much for long reply. I don't have dedicated server so i can't use first solution, but i think i'll have more luck with load test. I found some microsoft program called "Web Application Stress Tool", so i'll try it. At least , i know where to search for answer. Thanks again.

You're welcome.

The profiler will help you know how much of a resource hog your code is. Because PHP is inherently a database scripting language you will want to focus on any queries that are being run as well. Indexing large tables that are queried often can greatly improve performance.


Sorry if I am pointing out the obvious...

Totally true...
In every script I've profiled, sql queries took between 40 and 60 % of the total run time.

This is where most of the optimizations should be done, and first targeted.

Usually a script not using any external resources like database or remote server will not consume much resources, unless it does image resizing or complicated math calculations. Most bottlenecks come from database usage and this should be optimized first of all.

One of the most common pitfalls in database administration is lack or inproper usage of indexes, while proper one can increase the performance of certain DB query up to twenty times - from 1 second to 0.05 second on highly loaded server.

If you use database with your scripts devote more time to database optimization, don't bother about the script itself.