JR2 FileDataStore#inUseMap  is currently a synchronized map and that at times causes contention concurrent env. This map is used for supporting the Blob GC logic for JR2.
With Oak this map content is not used. As a fix we can either
- Set inUseMap to a Guava Cache Map which has weak keys and value
- Set inUseMap to a no op map where all put calls are ignored
- Modify FDS to disable use of inUseMap or make usesIdentifier protected
#3 would be a proper fix and #2 can be used as temp workaround untill FDS gets fixed