Each update to the repository creates a new content revision. As a result, with each update the size of the repository grows. To avoid uncontrolled repository growth, old revisions need to be be cleaned up to free disk resources. This maintenance functionality is called Revision Cleanup. It has been available as an offline routine since AEM 6.0.
With AEM 6.3 an online version of this functionality called Online Revision Cleanup was introduced. Compared to Offline Revision Cleanup where the AEM instance has to be shut down, Online Revision Cleanup can be run while the AEM instance is online. Online Revision Cleanup is turned on by default and it is the recommended way of performing a revision cleanup.
How to Run Online Revision Cleanup
Online Revision Cleanup is configured by default to automatically run once a day on both AEM Author and Publish instances. All you need to do is define the maintenance window during a period with the least user activity.
Full And Tail Compaction Modes
AEM 6.4 introduces two new modes for the compaction phase of the Online Revision Cleanup process:
The full compaction mode rewrites all the segments and tar files in the whole repository. The subsequent cleanup phase can thus remove the maximum amount of garbage across the repository. Since full compaction affects the whole repository it requires a considerable amount of system resources and time to complete. Full compaction corresponds to the compaction phase in AEM 6.3.
How To Configure Full and Tail Compaction
The default configuration runs tail compaction on week days and full compaction on Sundays. The default configuration can be changed by using the new configuration value full.gc.days of the RevisionCleanupTask maintenance task .
When you configure the full.gc.days value be aware that full compaction will run during the day(s) defined in the value and tail compaction will run during the days that are not defined in the value. For example, if you configure full compaction to run on Sunday then tail compaction will run Monday to Saturday. If, for example, you configure full compaction to run every day of the week then tail compaction will not run at all.