Reducing SQL queries in WordPress Templates

May 12th, 2010

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">
<?php apply_filters('the_content', ''); ?>
<?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.

By Martin

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