ldb 2.0.0 and above (Samba 4.11) introduced with LMDB as feature allowing the search of a range of values. This is useful in handling the usnChanged <= X query used in GetNCChanges in particular.
There is a small memory leak of the index key each time the query is run.
Mailing list reference: https://lists.samba.org/archive/samba/2020-February/228380.html
Merged into master as 535debb3 for Samba 4.13