All collections are loaded lazily by default.
MapDB never loads full collection into heap memory,
only small currently used portion (typically single tree node) is loaded into heap.
But even single tree node can be too large (for example 32 key-value pairs),
and you may want to load even single values lazily.
boolean valuesStoredOutsideNodes = true;
Map map = db.createTreeMap("name",32, valuesStoredOutsideNodes, false, null, null, null);
map.put("key","this string is loaded lazily with 'map.get(key)' ");