I have a Drupal 7 site which requires flushing the cache from time to time. The problem is that whenever I flush the cache (~30 seconds) the site is non-responsive until the flush is over.

What could be the cause and how do I debug this? Thanks

  • There can be multiple problems for this, huge database size, large number of modules, huge number of content, etc. You'll have to check through various scenarios. – Yogesh Dec 20 '16 at 9:02
  • The database is ~150mb, the site is modest. As I understand clearing the cache should never cause the site to become unresponsive, maybe just slow it down a bit. – Livshin Dec 20 '16 at 9:20
  • Maybe a list of used modules? – kwoxer Dec 20 '16 at 13:57
  • many of them. Some custom made.. Main one is ubercart for eCommerce. How would you debug? – Livshin Dec 20 '16 at 15:28

Using a MySQL frontend like phpMyAdmin run SHOW PROCESSLIST while your site is locked from the cache clear. That should show what is causing the issues for you. My guess is it will be a metadata lock. https://www.drupal.org/project/apdqc was built to prevent db locks in database caused by the cache.

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