- Why Cache?
- When to cache? (settings)
- How does the auto cache work?
- Cache Storage
- Cache Log
- Cache Status
- On demand refresh (admin or public)
Cacheing is required because:
- we want to display, query, filter and sort the data BUT
- some plugins that create user data do it in ‘funny’ non wp standard ways
- they stick all their user data in one user-meta record, sometimes as an object, sometimes as an array…. (eg: ym (yourmembers), although they appear to be moving to standard wp), so we cannot simply ‘select where meta = ‘
- they store their user data in non wp tables, so that data has to be fetched separately. This also means that the wp user update actions don’t fire. So any recaching dependent on that may not happen.
So the plugin grabs, extracts, does some magic and stores the data in a separate generic cache table. Originally this was aimed primary at csv extraction.
When to cache? (settings)
Ideally the lists should be up to date when you see them. BUT for reasons above this may not always be possible. So consider the following scenarios:
Internal admin access only?
- Consider switching off ALL auto caching.
- Only rebuild the data when you view the list.
Public lists, high level of user updates?
- Strongly suggest do NOT recache on every user update
- Cache at the greatest possible interval (less demand on sql database) – maybe daily ?
- Manual refresh can be made available via an icon link on user list page – see admin refresh link.
Public lists, very low level user updates?
- you must be sure about what plugins are causing user or user meta updates. If you have a plugin that is tracking the pages people view, or their logins and storing the data in the user meta… do I need to say more? Re caching on every user update would place a huge sql demand on your system.
- Consider caching on use update only – no scheduled caching.
How does the auto cache rebuild work?
(version 3.4.9 at time of writing)
The cache can be set to automatically update in the ‘background’. This is achieved using standard wordpress cron features. If you are new to cron, then basically all you need to know is that it needs some activity on your website to run. eg: a page request. A scheduled job will only run on the first page request after the jobs scheduled time. If you have a very low traffic site, this could be quite late.
A cache update request is initiated via cron on the following wordpress actions:
- add_action(‘deleted_user’,’amr_user_change’); // also for wpmu
If your install has a user update that does NOT trigger a wordpress action (eg: another plugin stores user data somewhere else), then the plugin has no way of knowing that a user update has happened.
If the other plugin uses its own update actions, you could add a custom function call on that action similar to the above calls.
Alternatively either a regularly scheduled update or a manual on demand refresh may be adequate.
The cache update request attempts to schedule a master cron job. Many of these wordpress actions may trigger within milliseconds of each other. The plugin therefore checks whether a cache update is scheduled within the near future to avoid duplicate work.
The master cron cache job then schedules individual jobs for each of the reports. They are scheduled to run separately, not concurrently. In your cron manager plugin you should see an entry for each job.
When testing, you should therefore do a page request or two approximately minutes apart for each report that you have designed. Check the cache log in between.
(version 3.4.9 at time of writing)
This may change at a later stage for installs that only use standard wordpress user meta. Other installs will need the current setupo to deal with their user data created by other plugins.
Currently a generic cache report table in csv format is created. This made sense originally, however as the plugin became popular more features were requested. This approach is not ideal for optimum efficiency (especially large high traffic installs). If one is only using standard wordpress user and user meta data, then the lists could be more efficient. To cope with non standard data, the curremt approach will have to continue.
The cache log will list the most recent cache rebuild activities. If you are concerned or not sure how the cache updates are initiated, please pay close attention to the cache log when testing. For more details see cacheing-the-cache-log
The cache status page lists
- the size (lines) of a list
- when the cached list was last built
- how long it took to build the cache
- the peak php memory requirement while running the cache update
- some info on the list
It also has options to totally clear out the various cache records (in case your install gets in a knot), and force the plugin to start again.