The revision cleanup is a required action for this release. Read here for a complete overview.
Update Oct 1, 2021:
R4J 4.5 revision data is not compatible with older versions of R4J
Known issue with MS SQL 2014/2016 databases. SQL Server error encountered when executing revision cleanup: “The query processor ran out of internal resources and could not produce a query plan...”.
This issue has been fixed in R4J 4.6.1, please upgrade your R4J version if you are affected.