AEM stores multiple revisions of content to enable rollback and version control. Over time, this accumulation of revisions can lead to significant disk space consumption. To address this, AEM offers Revision Cleanup, a process that reclaims disk space by removing old revisions.
Types of Revision Cleanup
Offline Revision Cleanup (Since AEM 6.0)
- Purpose: Performs a more thorough cleanup of the repository by removing older revisions that may not be cleaned by the online process.
- Process: Requires downtime, as the repository is taken offline. It performs a deep clean, which can reclaim more space and improve performance.
- Usage: Typically run during maintenance windows when the system can be taken offline, ensuring a comprehensive cleanup. Maintains only one generation of revisions. Used in exceptional cases, like storage space crunch or major upgrades.
Online Revision Cleanup (Since AEM 6.3)
- Purpose: Automatically removes old, unused revisions (data versions) in the repository during normal operation without downtime.
- Process: Runs periodically in the background, identifying and cleaning up unnecessary revisions to optimize storage and maintain repository performance.
- Usage: Suitable for production environments as it doesn’t interrupt normal operations. Maintains two generations of revisions, allowing for rollbacks.
Revision Cleanup Process
Regardless of whether it’s online or offline, the cleanup process involves three phases –
| Estimation | Evaluates the potential space savings from removing old revisions. Decide if proceeding with compaction is beneficial. |
| Compaction | Rewrites segments and tar files, excluding unused content. Creates a more compact representation of the repository. |
| Cleanup | Removes old segments and garbage data. Frees up disk space. |
Best Practices
- Schedule online revision cleanup regularly. This prevents excessive disk space consumption.
- Regularly check disk space to identify potential issues.
- If disk space is critically low and online cleanup is insufficient, offline cleanup can be considered.
- Always create a backup of your AEM instance before performing any cleanup.
- Online revision cleanup can impact performance. While it runs in the background, it might affect system performance during peak hours.
- Offline cleanup is a more time-consuming process. It requires careful planning and coordination.
Key Differences
| Feature | Offline Revision Cleanup | Online Revision Cleanup |
|---|---|---|
| AEM Instance | Shutdown required | No shutdown required |
| Space Reclaimed | More | Less |
| Complexity | High | Low |
| Frequency | Infrequent | Regular |
| Generations Kept | One | Two |
Further References
- https://experienceleague.adobe.com/en/docs/experience-manager-65/content/implementing/deploying/deploying/revision-cleanup
- Checkout our other blogs on similar knowledge on Working with AEM
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