Check this to understand Cron http://drupal.org/handbook/modules/system

-----Original Message----- From: Rajaram Shyamala [mailto:shyamala@netlinkindia.com] Sent: Tuesday, April 20, 2010 6:22 AM To: 'support@drupal.org' Subject: RE: [support] When are Caches Cleared?

Some links that will help you understand Caching and performance in Drupal.

http://www.lullabot.com/articles/a_beginners_guide_to_caching_data http://drupal.org/node/326504

Shyamala -----Original Message----- From: support-bounces@drupal.org [mailto:support-bounces@drupal.org] On Behalf Of Earnie Boyd Sent: Tuesday, April 20, 2010 3:36 AM To: support@drupal.org Subject: Re: [support] When are Caches Cleared?

Fred Jones wrote:

Running cron apparently does not clear the cache tables: http://drupal.org/node/315303

Is there any time period when caches are automatically rebuilt? I googled and can't find an answer to this seemingly-simple question.

Thanks.

Your question is vague. There are different types of "caches". Those that are true "caches" have an expiration field that control the rebuild of the cached data. If you mean the menu, well, it really isn't a cache even though it's rebuild is triggered by the "Clear cached data" button. The menu router data doesn't change unless you add a new module. The custom menu is handled slightly differently than the menus coming from modules but still the menu router doesn't change once you've set the menu.

Why do you ask? Are you developing code and not seeing the caches change or is there some production issue you need resolved?