add option to disable db cache

mhdb.py

@@ -46,12 +46,14 @@ def get_rank(hub, stars):
 
 
 class MHDB(object):
-    def __init__(self, path):
+    def __init__(self, path, use_cache=True):
         self.conn = sqlite3.connect(path)
         self.conn.row_factory = sqlite3.Row
+        self.use_cache = use_cache
         self.cache = {}
 
     def _get_memoized(self, key, query, *args):
+        if self.use_cache:
             if key in self.cache:
                 v = self.cache[key].get(args)
                 if v is not None:
@@ -59,7 +61,9 @@ class MHDB(object):
             else:
                 self.cache[key] = {}
         cursor = self.conn.execute(query, args)
-        v = self.cache[key][args] = cursor.fetchall()
+        v = cursor.fetchall()
+        if self.use_cache:
+            self.cache[key][args] = v
         return v
 
     def get_item_names(self):