performance

I have been searching for a good server monitoring solution for a while so that I can keep an eye on some of the servers that I run. Tools like Smokeping, Cacti and Nagios seemed promising at the outset, but they are more concerned with bandwidth and server status, not how the server is running. What I really needed was a way to find out how much memory a server was using, how many Apache requests were being made, what the average load of the server was, and also some way of letting me know when things were under strain.

I was at a meeting of the Manchester Web Performance Group the other day where Tom Taylor gave a talk about some of the performance testing tool he uses at Laterooms.com. He used a ruby script to set up some preferences in Firefox which then ran Selenium to open some web pages and test them with YSlow. The results of the YSlow inspection are then sent to a Show Slow server where the results can be graphed over time. I realise that I've just mentioned a whole stack of technologies there, so let me pick out the important ones:

Selenium is a remote control agent for web browsers, although it is most stable in Firefox. I have written about this tool before but it allows us to automate interaction with a website via a series of selenium scripts. These scripts can be exported into different code formats, including PHP.

Sometimes is is necessary to see how long your PHP code runs for. This can be done using the following function and examples. This will convert the result of the php function microtime() into a float value.

function getmicrotime($t){
  list($usec, $sec) = explode(" ",$t);
  return ((float)$usec + (float)$sec);  
}

Use this function to see how long something runs for. At the start of the code call the microtime() function and store the result at the start. At the end store the result of the microtime() function as the end and then use the two values to figure out how long the code took to run.