Only vacuum db if anything was written.

MosDb.py

@@ -9,12 +9,14 @@ class MosDb():
         self.conn = sqlite3.connect(self.dbfile)
         self.c    = self.conn.cursor()
         self.c.execute("PRAGMA foreign_keys=on;")
+        self.changes_made = False
 
     def commit(self):
         self.conn.commit()
 
     def finish(self):
-        self.c.execute("VACUUM")
+        if self.changes_made:
+            self.c.execute("VACUUM")
         self.conn.commit()
         self.conn.close()
 
@@ -29,6 +31,7 @@ class MosDb():
     def add_new_id(self, table, col, value):
         self.c.execute("INSERT INTO " + table + " (" + col + ") VALUES (?)", (value,))
         self.conn.commit()
+        self.changes_made = True
         rid = self.c.lastrowid
         self.idcache[table][value] = rid
         self.ridcache[table][rid]  = value
@@ -87,6 +90,7 @@ class MosDb():
             "INSERT OR REPLACE INTO " + table + " (" + fieldsList + ") VALUES (" + placeHolders + ")",
             valuesTuple
         )
+        self.changes_made = True
 
     def mark_deleted(self, objData):
         """Sets the isDeleted column to 1 for the specified object.
@@ -98,6 +102,7 @@ class MosDb():
             "UPDATE mosobjects SET isDeleted=1 WHERE mosId=? AND objId=?",
             ( self.get_mos_id(objData["mosId"]), objData["objId"] )
         )
+        self.changes_made = True
 
     def add_or_replace(self, objData):
         insertObj = {