Tuesday, 10 September 2013

Testing Server Load Before Running Plugin Code On Wordpress

Testing Server Load Before Running Plugin Code On Wordpress

UPDATED - 10th Sep 2013

I have updated this function to handle issues on Windows machines in which the COM object might not be created due to security issues.

If you have a underpowered Linux server and run the bag of shite that is the WordPress CMS system on it then you will have spent ages trying to squeeze every bit of power and performance out of your machine.

You've probably already installed caching plugins at every level from WordPress to the Server and maybe even beyond....into the cloud....all stuff normal websites shouldn't have to do but it seems WordPress / Apache / PHP programmers love doing.

A fast optimised database, queries that return data in sets (not record by record) and some static pages for content that doesn't change constantly should be all you need but it seems that this is not the case in the world of WordPress!

Therefore if you have your own server or virtual server and the right permissions you might want to consider implementing some code in important plugins that prevents the job you intend running causing more performance problems if the server is already over loaded.

You can do this by testing for the current server load, setting a threshold limit and then only running the code you want if the server load is below that limit.

Of course security is key so lock down permissions to your apps and only let admin or the system itself run the code - never a user and never by a querystring that could be hacked!

The code is pretty simple.

It does a split for Windows and non Windows machines and then it checks for a way to test the server load in each branch.

For Windows it has two methods, one for old PHP code and one for PHP 5+.

In the Linux branch it tests for access to the /proc/loadavg file which contains the current load average on LINUX machines.

If it's not there it tries to access the shell_exec function (which may or may not be locked down due to permissions - up to you whether you allow access or not) and if it can run shell commands it calls the "uptime" function to get the current server load from that.

You can then call this function in whatever plugin or function you want and make sure your server isn't already overloaded before running a big job.

I already use it in all my own plugins, the Strictly Google Sitemap and my own version of the WP-O-Matic plugin.


/**
 * Checks the current server load
 *
 * @param boolean $win
 * @return string 
 *
 */
function GetServerLoad(){

 $os = strtolower(PHP_OS); 
 
 // handle non windows machines
 if(substr(PHP_OS, 0, 3) !== 'WIN'){
  if(file_exists("/proc/loadavg")) {    
   $load = file_get_contents("/proc/loadavg"); 
   $load = explode(' ', $load);     
   return $load[0]; 
  }elseif(function_exists("shell_exec")) {     
   $load = @shell_exec("uptime");
   $load = explode(' ', $load);        
   return $load[count($load)-3]; 
  }else { 
   return false; 
  } 
 // handle windows servers
 }else{ 
  if(class_exists("COM")) {     
   $wmi  = new COM("WinMgmts:\\\\."); 
   if(is_object($wmi)){
    $cpus  = $wmi->InstancesOf("Win32_Processor"); 
    $cpuload = 0; 
    $i   = 0;   
    // Old PHP
    if(version_compare('4.50.0', PHP_VERSION) == 1) { 
     // PHP 4      
     while ($cpu = $cpus->Next()) { 
      $cpuload += $cpu->LoadPercentage; 
      $i++; 
     } 
    } else { 
     // PHP 5      
     foreach($cpus as $cpu) { 
      $cpuload += $cpu->LoadPercentage; 
      $i++; 
     } 
    } 
    $cpuload = round($cpuload / $i, 2); 
    return "$cpuload%"; 
   }
  } 
  return false;     
 } 
}

A simple server load testing function that should work across Windows and Linux machines for load testing.

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