XHProf in 30 Seconds: How to get started profiling PHP
The task was simple: I wanted to run xhprof (the Facebook-developed PHP profiler) to get some quick-and-dirty metrics on a PHP script. While xhprof is actually really easy to install and use, I had to read a surprising amount of material in order to run a simple install and write three lines of code.
To spare others the agony of cruising old Facebook docs in the Internet Archive, here's a 30 second guide to installing and using xhprof.
Installation
Install using pecl (You may need to use sudo):
$ sudo pecl install xhprof
It may tell you that you must install a specific version: sudo pecl install xhprof-0.9.2.
Once it's installed, you will need to tell PHP to use it. On Ubuntu, I created /etc/php5/apache2/conf.d/xhprof.ini with one line:
extension=xhprof.so
To get it working with Apache, restart Apache: sudo service apache2 restart.
Using
Usage is simple. To start profiling, add this to your script:
<?php
xhprof_enable(XHPROF_FLAGS_CPU + XHPROF_FLAGS_MEMORY);
?>
To stop the profiler and collect the data, try this:
<?php
$prof = xhprof_disable();
?>
The $prof data is just an associative array with function call names as the key and performance information as the value.
Making Sense of the Data
Here's a print_r() dump of a simple script with one function: test().
Array
(
[main()==>test] => Array
(
[ct] => 1
[wt] => 132
[cpu] => 0
[mu] => 1072
[pmu] => 0
)
[main()==>xhprof_disable] => Array
(
[ct] => 1
[wt] => 1
[cpu] => 0
[mu] => 1080
[pmu] => 0
)
[main()] => Array
(
[ct] => 1
[wt] => 167
[cpu] => 0
[mu] => 4160
[pmu] => 0
)
)
Each entry gives the following information:
- ct: Count. The number of times the function was called.
- wt: Wall Time. Amount of "real world" time (from "wall clock time").
- cpu: Number of CPU "ticks" executed for this function (a measure of CPU usage).
- mu: Memory usage
- pmu: Peak Memory Usage (a la
get_peak_memory_usage()). This does not always seem to be accurate,
There is a built-in Web UI for xhprof, but I haven't yet tried it.
If your French is better than mine, I recommend this presentation.
