Presentation from webinar held on August 19th, 2020, with Xdebug developer Derick Rethans and Seravo CEO Otto Kekäläinen. This presentation shows you how to use Xdebug (which is very easy with the Seravo WordPress development environment!) to make a record of what the WordPress PHP code does during a website page load, and how to use that information to optimize the performance of your WordPress site. For a video recording and Dericks presentation see https://seravo.com/blog/webinar-xdebug-profile-php/

1. Use Xdebug to profile PHP

2. Premium hosting
and upkeep for
WordPress
HTTP/2
TESTED
UPDATES
24/7 UPKEEP

3. Top-notch performance
A comparison published by a
Google employee at
ismyhostfastyet.com
confirms that Seravo’s
customer sites load faster
than competing services’.
The study used
time-to-first-byte (TTFB)
measurement data from real
users as collected from the
Chrome browser UX data. Fast/Average/Slow TTFB by WordPress Host

4. Seravo recommends Xdebug
● Xdebug is open source: github.com/xdebug/xdebug
● Embraced by the PHP community
● Plenty of features: profiling, stack traces, debugging..
● Included in Linux distributions, easy to install
● Pre-installed in many development environments
○ Varying Vagrant Vagrants (for WordPress core contributors)
■ xdebug_on
○ Seravo WordPress Vagrant and Docker images (for Seravo’s customers)
■ wp-xdebug-on

5. What on earth is PHP doing?!
Finding the code bottlenecks is
hard without proper tools.
Solution:
● Profile PHP code with
Xdebug
● Browse results with
Webgrind
● Visualize code path with
Gprof2dot and Dot

6. All WordPress site
developers should learn
Xdebug
It is
easy!

7. Very easy with Seravo WordPress dev
● Enable by running: wp-xdebug-on
● Run profiler on any URL easily by appending one
parameter
○ E.g. https://wordpress.local/?XDEBUG_PROFILE
● Files are generated at /tmp/cachegrind.out.x.y.z
● Browse results with Webgrind
○ E.g. http://wordpress.local/.seravo/webgrind/
Documentation at seravo.com/docs/development/xdebug/

8. DEMO

9. Typical issues: database
Typically developers don’t test
their plugins with large amounts
of data and they work well on
small sites.
As sites grow, all problems related
to excess data manipulation
become visible.
Solution:
● Inject more data on a test site
and see how it behaves.
● In code, don’t fetch
everything from the database.
Remember LIMIT in SQL and
posts_per_page in WP_Query.
● Design code to fetch only
what is needed for the view,
nothing else.

10. Switch to
Polylang
for faster
page loads

11. Typical issues: HTTP requests
External API calls in PHP
typically also block the entire
site from loading if the
external API is down.
Solution:
● Review use of wp_remote_get(),
fopen() and similar
● Store result and avoid re-fetching it all
the time using WP Transients API

12. Use WP Transients API
Store the result of a heavy/slow computation to avoid having to do it all
the time (e.g. HTTP requests or heavy database queries):
More at: seravo.com/blog/faster-wordpress-with-transients/
and developer.wordpress.org/apis/handbook/transients/

13. Extra helper: wp-speed-test
vagrant@development:~$ wp-speed-test
Testing speed URL https://wordpress.local...
For an explanation of the different times, please see docs at https://curl.haxx.se/docs/manpage.html
URL TOTAL NAMELOOKUP CONNECT APPCONNECT PRETRANSFER STARTTRANSFER = AVG
https://wordpress.local 0.179 0.004 0.004 0.014 0.014 0.179 0.179
https://wordpress.local 0.154 0.000 0.000 0.000 0.000 0.154 0.167
https://wordpress.local 0.157 0.000 0.000 0.000 0.000 0.157 0.164
https://wordpress.local 0.167 0.000 0.000 0.000 0.000 0.167 0.164
https://wordpress.local 0.163 0.000 0.000 0.000 0.000 0.162 0.169
https://wordpress.local 0.147 0.000 0.000 0.000 0.000 0.147 0.168
https://wordpress.local 0.169 0.000 0.000 0.000 0.000 0.169 0.168
https://wordpress.local 0.178 0.000 0.000 0.000 0.000 0.178 0.168
https://wordpress.local 0.167 0.000 0.000 0.000 0.000 0.167 0.168
Test completed. If the values seems too high, please profile your PHP code to find potential
bottlenecks. Note that this test tells how fast your site is in the sense of how long it takes for PHP
to generate the HTML output. To test how much load the site can handle, run wp-load-test.

14. Hunt for random slowness
$ wp-speed-test https://wordpress.local/hello-world/?XDEBUG_PROFILE
Testing speed URL https://wordpress.local/hello-world/?XDEBUG_PROFILE...
For an explanation of the different times, please see docs at https://curl.haxx.se/docs/manpage.html
URL TOTAL NAMELOOKUP CONNECT APPCONNECT PRETRANSFER STARTTRANSFER = AVG
https://wordpress.local/hel... 0.637 0.004 0.004 0.013 0.013 0.636 0.637
https://wordpress.local/hel... 0.469 0.000 0.000 0.000 0.000 0.468 0.553
https://wordpress.local/hel... 0.512 0.000 0.000 0.000 0.000 0.511 0.539
https://wordpress.local/hel... 0.484 0.000 0.000 0.000 0.000 0.483 0.525
https://wordpress.local/hel... 0.483 0.000 0.000 0.000 0.000 0.482 0.517
https://wordpress.local/hel... 0.556 0.000 0.000 0.000 0.000 0.555 0.524
https://wordpress.local/hel... 0.910 0.000 0.000 0.000 0.000 0.908 0.640
https://wordpress.local/hel... 0.496 0.000 0.000 0.000 0.000 0.495 0.633
https://wordpress.local/hel... 0.475 0.000 0.000 0.000 0.000 0.474 0.625
16 MB

15. Always remember to measure
before and after!

16. seravo.com/docs
Instructions for
WordPress site
developers

17. Lots of tips out there!
The database is often the
performance bottleneck. See my
other talk on WordPress and
database optimization:
More in-depth code profiling tips
in my WordPress performance
talk:
wordpress.tv/?s=otto+kekäläinen

18. See also
Make Your Site Faster with Caching
https://seravo.com/blog/wordpress-cache/
300% faster WordPress load times with transients
https://seravo.com/blog/faster-wordpress-with-transients/
5 common reasons why your WordPress site is slow
https://youtu.be/8sJExUO-U4A
Improving WordPress Performance with XDebug and PHP Profiling
https://youtu.be/oKcIS5A-6_c

19. Thank you!
Seravo.com @Seravo @ottokekalainen