With JCR observation any JCR repository offers a really nice feature to react on any changes in the repository. Because the mechanism is quite powerful and easy to use, it has found many adopters which work with it.
If you have worked with that feature and also imported large amount of content, you might also encounter the problem that there is a delay between persisting a change in the repository and the time, when the observation event for this change is fired. This delay is mainly based on the number of registered observation handlers and the time these handlers require to process the event (the whole JCR observation events are handled by a single thread). If it takes 100ms to run through all handlers and you persist 10k changes in 2 minutes, it will pill up and take about 20 minutes until the queue is empty again.
This delay may harm your application and user experience, so it’s advisable to
- improve the processing speed of any JCR event handler
- keep the queue small.
Especially if you have jobs, which are not time critical but might cause a storm of events (e.g. data importers), you should be aware of this and add artificial pauses to your job, so the observation event queue will not get too large.
A simple tool to help has been added to CQ/AEM 5.6.1, it’s called JCR Observation throttle (see http://dev.day.com/docs/en/cq/current/javadoc/com/day/cq/commons/jcr/JcrObservationThrottle.html)
It allows you to wait until all pending events in the observation queue have been delivered. This helps you to wait for quiet moments and then start your data import. But be careful, the delay might be very long, if other processes constantly interfere.