I’ve been making some changes to this site recently: upgrading to the newest version of WordPress, choosing a new theme and fiddling with the layout.

One thing I discovered is that, unless you’re running a very minimal installation, it’s quite easy to run out of memory, even with only a handful of plug-ins. Versions of the software have become slightly larger since WordPress 2.6 or so, plus plug-ins have become more ambitious, not to mention the increased usage of rich content like videos and AJAX transitions.

Every time I tweaked something, I ended up with blank pages and an error message like this:

Fatal error: Allowed memory size of X bytes exhausted (tried to allocate X bytes) in /home /Your-Username/public_html/ the particular folder on line X

I searched around for quite some time for advice, and tried each of the following, before ending up at a working solution. They didn’t work for me, but I’ll leave them here since they might prove useful for someone else. Please be very careful, though: some of these ‘handy tips’ will break your entire site.

1) De-activating all but the most essential plug-ins. This is probably good housekeeping advice all-round, but didn’t actually make a lot of difference. The basic install was using 26MB of the 32MB allocated; with a full suite of plug-ins it was just over 28MB. Add some users, and you’ll quickly run out of memory — the extra 2MB from disabling plug-ins didn’t make enough difference.

2) Alter the value of php_value memory_limit in your .htaccess file. Doing this broke the whole site: YMMV.

3) Optimise your database tables using phpMyAdmin. Saved about 200KB. Woop.

4) Adding the line “memory_limit = 64M” in my php5.ini file. Made no difference one way or another.

What actually worked was this.

Open wp-config.php and find this bit:

/** Sets up WordPress vars and included files. */
require_once(ABSPATH . 'wp-settings.php');

Change it so that it reads like this:

/** Sets up WordPress vars and included files. */
define('WP_MEMORY_LIMIT', '64M');
require_once(ABSPATH . 'wp-settings.php');

Touch wood, that’s done the trick. The site’s still as slow as molasses, of course, but at least I’m not running out of memory.