Varesano.net

A filter is a Drupal feature, usually implemented by some contributed modules, which substitutes parts of a node text with some other text.

Eg: if you use the Path filter module you can insert links like:

<a href="internal:node/25">hello!</a>

and the string internal:node/25 will be substituted by something like http://www.example.com/node/25 where www.example.com is your website url.

In order to save server's resources, Drupal caches this filtering transformations at each node update. This way the filters logics are executed only when a content is updated.

Sometimes you might want to invalidate all the filter cache entries so that every filter will be rerun on the next node view.

In order to do this you can execute this query on your drupal database:

delete from cache_filter;

Be careful: this will delete the whole filter cache and might affect your website performance if you have a huge website with lot of filters enabled. Anyway performance issues will disappear as soon as cache is regenerated.