This is an updated Tar Compaction and Garbage Collection process based on AEM 6.4. This maintenance functionality is now called Revision Cleanup.
The AEM platform is based on Apache Jackrabbit Oak. Oak is an effort to implement a scalable and performant hierarchical content repository for use as the foundation of modern world-class web sites and other demanding content applications. It uses TarMK, a fast, small and simple embedded hierarchical database engine serving as a persistence backend for the Java Content Repository (JCR). It implements multi-version concurrency control (MVCC) and stores all data in tar files in an append only way. And because of this MVCC persistence of only appending, it is critical to perform scheduled maintenance activities in keeping a performant and efficient AEM system. The lack of these maintenance tasks causes instability, performance and disk space issues and outages.