Reducing SQL queries in WordPress Templates

If you work on a busy WordPress sites in a shared hosting environment, you know how important is to keep the number of MySQL queries down as much as possible. Even if you are using some caching plugin, it's a matter of principle.

Today I was shocked to see that one of my WordPress templates (it's based on Cutline template) is taking more than 100 queries on the index page. I was removing various parts of the template until I found that it's the the_tags() WordPress template tag.

This is the important part of the template:

<div class="entry">
<?php the_excerpt(); ?>
</div>	

<div class="postmetadata">
<p><?php the_tags( 'Tags: ', ', ', ' | ' ); ?></p>
</div>	

And here's a number of queries going on on my test site right now with this code:

Total Time: 78 database queries run in 0.014724969863892 seconds.

Finally I discovered that if I replace the_excerpt() with the_content() (that means the full articles are displayed, not just first few sentences), the queries go down to around 50. Is the_tags() not working with database cache and global PHP object until the whole content is shown?

I found the exact line in the_content() function which makes this happen and put it into my code, right before the_excerpt:

<div class="entry">
<strong><?php apply_filters('the_content', ''); ?></strong>
<?php the_excerpt(); ?>
</div>	

<div class="postmetadata">
<p><?php the_tags( 'Tags: ', ', ', ' | ' ); ?></p>
</div>	

Now here's the number of SQL queries: 

Total Time: 47 database queries run in 0.0041866302490234 seconds.

That means the_tags() won't take any extra queries now. Interesting! If you are developing templates, watch out for this.

The plugin I used to get the exact number of queries is WPDB Profiling.

Martin Viceník

Martin graduated as an engineer in Computer Science from Slovak Technical University in Bratislava. He grew up in Liptovský Mikuláš in northern Slovakia next to the beautiful Tatra mountains. He is the developer behind our FV Player.