How to hunt for WordPress performance hogs

So after my previous post on how I discovered my major causes of wordpress pain, I kept looking on what is causing my other delays. Eventually, while looking at my source code, I discovered that my wordpress page was always reporting how many SQL queries it took and how long they took to complete. Looking at the footer, this was done by this command:

<?php echo get_num_queries(); ?> queries. <?php timer_stop(1); ?> seconds

Now, I understood that this was very helpful but I couldn’t understand why it was returning a time like 10 seconds when the page was loading for 4-5. A quick google search for this code however did lead me to a page that was explaining how to Keep WordPress overhead down. Through there, I realized that those seconds were some sort of CPU time taken to draw those queries.

Through this then, I now had a semi-accurate way to monitor the impact of each plugin on my site. I only needed to figure out which parts of the site were hogging down the queries and increasing the load time.

I created a quick table in a Spreadsheet and started logging down the differences.

  • First, I made the performance text visible, so that I don’t have to look at the source code each time (You can still see it by scrolling to the bottom of the page)
  • I disabled the WP-Cache so that the queries are done every time
  • I then started disabling each plugin in turn and reloading a page. Then I compared that with the previous loading time (where the plugin was enabled.) I noted down the difference in queries and the average/approximate CPU time difference.

Unfortunately since the CPU time tended to vary from load to load, I couldn’t get an accurate number of the difference. The table I made in the end looked something like this

Plugin name Queries CPU Time Taken
Bad Behaviour 1 5
Hide Text 0 Negligible
Greeklish 0 Negligible
One click install 0 Negligible
SimplePie WordPress Plugin 4 Negligible
Security Scan 1 1

After I went through all the plugins, then I started doing the same thing with my various widgets and snippets of code in my theme that might be causing this.

Once this was done, I had one likely suspect plugin and a few widgets that were probably contributing to this slowdown. You see, my theme, a very heavily hacked HemingwayEx, was using some custom widgets in order to draw from WordPress the latest comments, recent posts and whatnot. These widgets queried the database each and every time a page would load which was quite frankly impractical.

Fortunately a short time before, I had discovered the very useful bundle of post plugins. They were also there to hunt for recent comments & posts and related posts and they also included a built-in caching mechanism! As sweet as it gets.

I quickly modified my widgets to run this code instead and the results were wonderful. By disabling also the single other plugin I found that was slowing things down, Bad Behaviour, I’ve now managed to drop the loading time considerably (or so it seems for the time being). Not only that, but I’ve managed to put a few new toys to use that do a better job than HemingwayEx’s built in functionalities.

Currently my site seems to load lightning fast compared to before but I’m not absolutely convinced this will not change once my shared hosting environment gets bogged down. Hopefully, even if that happens I will still have a much much better performance than before.

I am still stuck at around 65-80 queries per page load but I can’t figure out where they come from. I am hoping that I’ll eventually be able to trace it but for now it seems enough.

Btw, I just loved the functionality of the Post Plugins to measure their own execution time and report it back to you. This is something that all plugins should be doing in order to give the web designer an idea on what is going on with his site. I’m going to work to see if I can implement that in the Lifestream plugin I’m working on and then see if I can place it on other plugin as well.

Btw (2), Can anyone explain why more people don’t take advantage of the Plugin cache plugin? I am fairly certain that a number of heavy plugins (like Popularity contest) could make good use of it.

As always, if you have any more ideas on where to look and tweak to improve my WP performance even more, I’ll be glad to hear them (AKA Whining because no one is commenting on my blog :P).

PS: It’s a pity that I had to disable Bad Behaviour as it worked quite well until now. I also don’t like to reply too much on just a single anti-spam plugin. Unfortunately, the performance hit was undeniable and I’d rather my site doesn’t take an extra 3-4 seconds to load every time.

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