Symptoms

This occurs a few days after restart

Exception in thread "DefaultQuartzScheduler_Worker-9" java.lang.OutOfMemoryError: Java heap space

Cause

The DefaultQuartzScheduler Thread is a scheduler thread that is responsible for scheduling activities such as confluence backups, indexes and sending mail and daily reports. An out of memory error in the DefaultQuartzScheduler Thread can kill it, hence it will not schedule the tasks.

Resolution

To resolve this problem,

1. Increase the memory allocated to your instance. See Fix java.lang.OutOfMemoryError in Confluence.
2. Fix your indices
   1. Stop your server
   2. Follow the instructions in Rebuilding index from scratch.
   3. Restart server. Also don't forget the manual re-index step that you need to perform in Confluence Admin > Content Indexing after having restarted the server.