Fixing out of memory problem for cron job

Drupal is known to be resource heavy system that heavily depends on database storage for content generation. While minimum recommendation for PHP memory limit is 32MB, it is not uncommon to allow as much as 128MB of RAM to PHP in bigger sites.

With tons of modules installed, Drupal cron job can fail due to lack of memory even with 128MB. Quick solution is to increase PHP memory limit. There are several ways to do it and they are well explained at http://drupal.org/node/207036.

However, it would not be ideal to increase memory for all page loads just because of cron job, when that much memory may not be needed for most of the time. I'd like to share couple of ways to give more memory to cron jobs only and not to other pages.

First method is to include a conditional in your settings.php. Cron job is either invoked by accessing /cron.php (usually by system's cron tab) or by manually visiting the page, admin/reports/status/run-cron. Hence,

There are bunch of calls to ini_set() function in settings.php and below them would be a good place to put the code. If you use Poorman's cron module instead of system cron tab to trigger Drupal cron periodically, it directly calls function to run cron hooks, drupal_cron_run(), and the method above will not work. Next suggested method will be useful for this case.

Second method is to write a custom module to implement hook_cron.

Drupal allows modules to assign themselves a weight to insure that their hooks are called before others. hook_install() can take care of assigning the weight. Attached is a little module that does the job. It is bare minimum and you will need to change hard coded value since it lacks UI admin setting to change memory limit.