Last year, an issue with Operations Manager DataWarehouse event grooming was discovered that was addressed in Microsoft System Center 2012 R2 Operations Manager
Update Rollup 7
(OpsMgr 2012 R2 UR7). This was an issue where dependent tables were not being groomed:
In a database, the grooming of certain MT$X$Y tables were missed because of the filtering logic, therefore the tables were never groomed.
In Data Warehouse, the grooming of certain tables was missed occasionally because current logic expects the rows to be returned in a certain order.
What’s important to note about this fix in UR7 is that it simply prevented the issue from continuing. It
delete any orphaned data that was already in the EventParameter tables. Because of this, you may still be seeing large EventParameter tables in your environment. If so, Microsoft’s own
has a great blog post where she’ll tell you how to get this cleaned up: