Troubleshooting PHP Performance in Microsoft Azure Web Sites with Xdebug

Slow application performance issues tend to be challenging to troubleshoot regardless of the platform in which your application is running. This is due in great part to the sometimes random nature of these issues. These types of issues also often do not result in a specific error being logged.

If you’re running PHP applications in Windows Azure Web Sites (such as WordPress or Joomla), the Xdebug extension can help you identify which function(s) or method(s) inside your application is taking a long time to execute.

Note: As with any other profiler, Xdebug profiling may have an impact on your website’s performance. Therefore, it’s not recommended to leave it enabled all the time. Enable it only while you are troubleshooting a specific issue and then disable it. If possible, always try to use the trigger optioned as detailed in Selectively Enabling Xdebug Using a Trigger later in this post.

Follow these steps to enable Xdebug and analyze the logs generated.

1. Download the non-thread safe version (identified by having ‘nts’ in the name of the file) of the Xdebug DLL file that matches the version of PHP and the bitness (32-bit or 64-bit) of the application that you are currently running in Windows Azure Web Sites. You can download the DLL from Xdebug’s download page at http://xdebug.org/download.php. For example, my website is running PHP version 5.5 and is running in 64-bit mode as shown below.

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Therefore, I need to download Xdebug using the link that says “PHP 5.5 VC11 TS (64 bit)”. When I click that link, it downloads a file called php_xdebug-2.2.3-5.5-vc11-nts-x86_64.dll. Notice that 2.2.3 represents the version of Xdebug, 5.5 is the version of PHP that this extension is intended for, nts stands for non-thread safe and x86_64 identifies it as the 64 bit version.

2. Connect to your website using FTP, GIT or WebMatrix. You can download WebMatrix here or you can click on the Dashboard tab of your Windows Azure Web Site portal and click on the WebMatrix icon (shown below) in the toolbar at the bottom of the page.

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3. Once connected to your website, create the following two folders if they don’t exist already:

• \bin
• \bin\xdebug_profiles

4. Copy the Xdebug extension that you downloaded in Step 1 to the \bin folder you just created.
5. Add a file called .user.ini (notice the dot at the beginning of the file name) to the root directory of your website.
6. Xdebug allows you to either leave it enabled or selectively enable it via a trigger in a query string. It’s preferable to enable Xdebug using a trigger, but if the issue happens randomly and it’s difficult to catch, you can leave it enabled and stop it once the problem has happened. Be aware, however, that doing so may cause you to experience performance problems, so you should test this carefully to see how it interacts with your application.

Select one of the following two methods:

Method 1: Leave Xdebug Enabled all the Time

Add the following lines to your .user.ini file (where zend_extension is pointing to the name of the xdebug dll you downloaded in Step 1):

zend_extension = ".\bin\php_xdebug-2.2.3-5.5-vc11-nts-x86_64.dll"
xdebug.profiler_enable=1
xdebug.profiler_output_dir="D:\home\site\wwwroot\bin\xdebug_profiles"

Note: Make sure you have enough space in your xdebug.profiler_output_dir as the amount of information generated by the profiler can be enormous for complex scripts. Also note that “site” in the output path should not be replaced with your particular site name.

Method 2: Selectively Enable Xdebug via a Trigger

Add the following lines to your .user.ini file (where zend_extension is pointing to the name of the xdebug dll you downloaded in Step 1):

zend_extension = ".\bin\php_xdebug-2.2.3-5.5-vc11-nts-x86_64.dll"
xdebug.profiler_enable=0
xdebug.profiler_output_dir="D:\home\site\wwwroot\bin\xdebug_profiles"
xdebug.profiler_enable_trigger=1

Note: If you use this option then you can leave Xdebug profiling OFF (set to 0) and then it can be triggered with a query string (e.g. http://<yoursite>/<pagename>.php?XDEBUG_PROFILE=1) to profile an individual request instead of profiling your whole site which will affect your website’s performance.

7. Open your website in the Windows Azure Portal, click on the Configure tab, scroll to the App Settings section and add a new key called PHP_ZENDEXTENSIONS with a value pointing to the location of the Xdebug dll copied in Step 4 as shown below.

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8. Click Save at the bottom of the page.

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9. If you are not enabling profiling using a trigger, wait for the problem to happen and then go to Step 10. If you are using a trigger to enable Xdebug profiling, when you notice your application is slow, enable Xdebug profiling by triggering it with a query string in the following form: http://<yoursite>/<pagename>.php?XDEBUG_PROFILE=1
10. All the files will be saved to the /bin/xdebug_profiles folder. The files will start with "cachegrind.out" and end with the PID (process ID) of the PHP-CGI process.
11. Download all the files via FTP using an FTP client like Filezilla. (For more information on accessing your website using FTP, see this blog post.)
12. Once you have collected the Xdebug logs, use WinCacheGrind to read the files and identify slow running methods. You can download WinCacheGrind from http://sourceforge.net/projects/wincachegrind/.
13. After opening the file, you will see a list of the pages and functions being called and the time spent on each. By drilling down into each parent function/method, you can identify which one(s) are taking the longest time. The screenshot below shows an example. Click the image for a larger image.

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14. Once you have identified the function/methods taking the longest time, the application’s developer should take look at the source code and try to understand why is taking that long and how can be improved.

References

· PHP Troubleshooting in Windows Azure Web Sites
http://ruslany.net/2013/01/php-troubleshooting-in-windows-azure-web-sites/

· How to Enable XDebug in Windows Azure Web Sites
http://blogs.msdn.com/b/silverlining/archive/2012/09/20/how-to-enable-xdebug-in-windows-azure-web-sites.aspx

· XDEBUG EXTENSION FOR PHP | DOCUMENTATION
http://xdebug.org/docs/profiler

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