Databases used by SharePoint have fragmented indices (SharePoint Server)
APPLIES TO: 
2013 2016 2019 Subscription Edition 
SharePoint in Microsoft 365
Rule Name: Databases used by SharePoint have fragmented indices.
Summary: SharePoint Server uses SQL Server to store most of the content for the Web site and configuration settings. One or more of the databases used by SharePoint Server have fragmented indexes. A fragmented index can cause a degrade in performance.
Cause: Database indexes can fragment over time as a result of insert and update operations performed by SharePoint Server. We recommend that you periodically delete and rebuild these indexes to improve system performance.
Resolution: Reorganize and rebuild indexes
- To correct index fragmentation, you can reorganize an index or rebuild an index. For more information, see Reorganize and Rebuild Indexes.