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Jawira Portugal
Jawira Portugal

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Profiling a PHP script with XDebug

Software profiling is a powerful technique when you want to optimize your code. Among other things, a profile snapshot will show you which parts of your software are the slower.

In this article I will explain how to create a profile snapshot for a PHP script.

Requirements

I assume you are using Ubuntu and you already have PHP installed. Please also install XDebug 3 and KCachegrind:

$ apt install php-xdebug
$ apt install kcachegrind
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Create profile file

As an example, I will profile tests from jawira/plantuml-encoding.

$ git clone https://github.com/jawira/plantuml-encoding.git
$ cd plantuml-encoding
$ php tests/vanilla.php
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Execute the following command to profile tests/vanilla.php:

$  php -dxdebug.mode=profile -dxdebug.output_dir=. tests/vanilla.php
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After the execution is finished, a new profile snapshot will be created. This profile file has the following name pattern cachegrind.out.xxxxx (where xxxxx is a number).

terminal screenshot

XDebug can be configured in php.ini. Here we have configured XDebug on-the-fly passing php.ini configuration through the terminal.

  • -dxdebug.mode=profile: This option makes profile mode enabled for this command.
  • -dxdebug.output_dir=.: Save profile snapshots in current dir ".", otherwise snapshots are saved in /tmp.

In our case profiling mode is ephemeral, but it can be a problem if you are activating profiling by other means (for example directly editing php.ini file). Profile snapshots can take a LOT of disk space, never leave profile mode permanently enabled.

Opening profile file

To visualize your profile snapshot, simply open the snapshot (in our case cachegrind.out.14476) with KCachegrind.

KCachegrind screenshot

The reading and interpretation of profiling files are beyond the scope of this article, yet I recommend you to see this video https://www.youtube.com/watch?v=h-0HpCblt3A presenting KCachegrind.

Conclusion

Creating a profile snapshot is easy if you understand how to configure XDebug properly. Using -d options is very convenient technique to enable profiling from the terminal.

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