improvement: better memory usage and admin commands to analyze it

src/database/abstraction.rs

@@ -38,6 +38,7 @@ pub trait KeyValueDatabaseEngine: Send + Sync {
     fn memory_usage(&self) -> Result<String> {
         Ok("Current database engine does not support memory usage reporting.".to_owned())
     }
+    fn clear_caches(&self) {}
 }
 
 pub trait KvTree: Send + Sync {