For performance reasons, Composr defines a number of caches. During normal operation of Composr, these caches should be unnoticeable; if things are being edited from outside Composr theoretically Composr will automatically pick up on it, but you may sometimes need to force a cache flush.

On a default install all recommended caches are enabled.

Some kinds of cache may be turned off in the configuration, but leaving them on gives vastly improved performance.

If you can identify a situation where you need to rebuild or empty a cache that should not exist, please report it as a bug.

Self-learning cache

The self-learning cache is quite a sophisticated cache mechanism to speed up Composr. It learns what resources are used by a page, and then bulk-loads them in the future.

The self-learning cache is most relevant when it comes to language strings. To avoid having to load up all the language files a page might use (language files are relatively monolithic, so inefficient to load), it will remember what strings are used by a page. Pages may use different strings when executed in different contexts, so the cache will always fall-back to loading the full language files if it has to, with those strings then also being added to the cache for the future. However, what if a page is referencing a string that does not exist? The self-learning cache would always be loading the full language files to try and hunt for it. This is why the cache also learns what strings are used by a page but do not actually exist even in the full language files. A ramification of this is that if you are developing and add the strings later, you will need to clear out the self-learning cache for Composr to be able to pick up on the new strings. Further, if you referenced language strings at any point while forgetting to first do a language file include, the self-learning cache will just figure these strings don't exist anywhere, even if you add the include later.

There are a number of optimisers:

• Correct MySQL schema issues – this is intended for programmers-only, you are very unlikely to need it.
• Optimise/fix database tables – this will try and fix some database tables and works with MySQL-only. If the database has become very corrupt, you may need to use a tool such as phpMyAdmin to repair a database from outside Composr.
• Broken URLs – this will look for broken URLs.
• Regenerate image thumbnails – this will regenerate all thumbnails (slow and probably not useful).
• Find orphaned uploads – find on-disk uploads that seem to no longer be referenced.
• Delete page access statistics – remove old page statistics to reduce database usage.

Frankly most of these optimisers are not useful. We provide them for very rare situations, or for helping programmers manage complicated operations.