+6030. [bug] Refactor the ADB to use a global LRU queue, store
+ the ADB names and ADB entries directly in the hash
+ tables instead of buckets, and properly clean the
+ ADB names and entries when not in use. [GL #3239]
+ [GL #3238] [GL #2615] [GL #2078] [GL #2437]
+ [GL #3312] [GL #2441]
+
6029. [cleanup] Remove the unused external cache cleaning mechanism
as RBTDB has its own internal cache cleaning
mechanism and we don't support any other database