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Debug slow PHP applications using IntelliJ or PHPStorm

It is frustrating when your PHP application is really slow and you do not know which part of your code is taking up too much time.

Google considers 2 seconds as the optimal loading time for a fast loading website.

Enabling PHP XDebug Profiler

PHP’s Xdebug extension can be used to profile your web requests and CLI requests and understand why they are slow and which method is causing the bottleneck.

Follow this link to install XDebug on the server on which your PHP application is running: https://xdebug.org/docs/install

Once XDebug is installed successfully, open the xdebug configuration file and add the following line:

xdebug.profiler_enable = 1

Once you add the above line, the configuration file should look like this:

vagrant@dev:/etc/php/7.2/cli/conf.d$ cat 20-xdebug.ini
zend_extension=xdebug.so
xdebug.show_error_trace = 1
xdebug.profiler_enable = 1

The above file only enables the profile for CLI requests. For enabling the profile for web requests, add the same line into the following file:

vagrant@dev:/etc/php/7.2/fpm/conf.d$ cat 20-xdebug.ini
zend_extension=xdebug.so
xdebug.show_error_trace = 1
xdebug.profiler_enable = 1

Once the files are saved, restart the PHP FPM service:

service php7.2-fpm restart

Now you can open your phpinfo file and verify if the profiler is now enabled:

Generating the profile file

You can now open the slow webpage and PHP XDebug will create a profiler in the profiler_output_dir mentioned above (i.e. ./tmp) which can also be customized in the xdebug ini file.

I opened the homepage of my PHP application and found these files in my /tmp directory:

root@dev:/tmp# ls cache* -gGltrh
-rw-r--r-- 1 1.6K Sep 23 10:29 cachegrind.out.3315.01c00e
-rw-r--r-- 1 1.2M Sep 23 10:29 cachegrind.out.3315
-rw-r--r-- 1 2.1M Sep 23 10:31 cachegrind.out.3312
-rw-r--r-- 1 1.8K Sep 23 10:31 cachegrind.out.3312.0df7d7
-rw-r--r-- 1 1.2M Sep 23 10:31 cachegrind.out.3315.05bc8d
-rw-r--r-- 1 1.2M Sep 23 10:31 cachegrind.out.3312.073921
-rw-r--r-- 1 2.0K Sep 23 10:31 cachegrind.out.3312.03dc36

Analyzing the generated files

Once these files are generated, you can open them in IntelliJ or PHPStorm for analysis:

Once you have finished the analysis, make sure to remove or comment the line xdebug.profiler_enable in both your ini files and restart your FPM service. Otherwise the tmp directory will get filled very quickly.

Other Free Tools

Apart from paid tools such as IntelliJ/PHPStorm, there are some free tools to analyze the generated cachegrind files:

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