Use NoDB by default

adds shortcuts, so you can specify "DictDB", rather than "full.path.to.DictDB".

IPython/parallel/apps/ipcontrollerapp.py

@@ -110,10 +110,11 b' flags.update({'
     'nodb' : ({'HubFactory' : {'db_class' : 'IPython.parallel.controller.dictdb.NoDB'}},
                     """use dummy DB backend, which doesn't store any information.
                     
-                    This can be used to prevent growth of the memory footprint of the Hub
-                    in cases where its record-keeping is not required.  Requesting results
-                    of tasks submitted by other clients, db_queries, and task resubmission
-                    will not be available."""),
+                    This is the default as of IPython 0.13.
+                    
+                    To enable delayed or repeated retrieval of results from the Hub,
+                    select one of the true db backends.
+                    """),
     'reuse' : ({'IPControllerApp' : {'reuse_files' : True}},
                     'reuse existing json connection files')
 })
@@ -138,7 +139,6 b' aliases = dict('
 aliases.update(base_aliases)
 aliases.update(session_aliases)
 
-
 class IPControllerApp(BaseParallelApplication):
 
     name = u'ipcontroller'

IPython/parallel/controller/dictdb.py

@@ -184,6 +184,10 b' class DictDB(BaseDB):'
         msg_ids = self._records.keys()
         return sorted(msg_ids, key=lambda m: self._records[m]['submitted'])
 
+NODATA = KeyError("NoDB backend doesn't store any data. "
+"Start the Controller with a DB backend to enable resubmission / result persistence."
+)
+
 class NoDB(DictDB):
     """A blackhole db backend that actually stores no information.
     
@@ -197,7 +201,7 b' class NoDB(DictDB):'
         pass
     
     def get_record(self, msg_id):
-        raise KeyError("NoDB does not support record access")
+        raise NODATA
     
     def update_record(self, msg_id, record):
         pass
@@ -209,8 +213,8 b' class NoDB(DictDB):'
         pass
     
     def find_records(self, check, keys=None):
-        raise KeyError("NoDB does not store information")
+        raise NODATA
     
     def get_history(self):
-        raise KeyError("NoDB does not store information")
+        raise NODATA
 

IPython/parallel/controller/hub.py

@@ -119,6 +119,13 b' class EngineConnector(HasTraits):'
     heartbeat=CBytes()
     pending=Set()
 
+_db_shortcuts = {
+    'sqlitedb' : 'IPython.parallel.controller.sqlitedb.SQLiteDB',
+    'mongodb'  : 'IPython.parallel.controller.mongodb.MongoDB',
+    'dictdb'   : 'IPython.parallel.controller.dictdb.DictDB',
+    'nodb'     : 'IPython.parallel.controller.dictdb.NoDB',
+}
+
 class HubFactory(RegistrationFactory):
     """The Configurable for setting up a Hub."""
 
@@ -181,8 +188,17 b' class HubFactory(RegistrationFactory):'
 
     monitor_url = Unicode('')
 
-    db_class = DottedObjectName('IPython.parallel.controller.dictdb.DictDB',
-        config=True, help="""The class to use for the DB backend""")
+    db_class = DottedObjectName('NoDB',
+        config=True, help="""The class to use for the DB backend
+        
+        Options include:
+        
+        SQLiteDB: SQLite
+        MongoDB : use MongoDB
+        DictDB  : in-memory storage (fastest, but be mindful of memory growth of the Hub)
+        NoDB    : disable database altogether (default)
+        
+        """)
 
     # not configurable
     db = Instance('IPython.parallel.controller.dictdb.BaseDB')
@@ -258,9 +274,9 b' class HubFactory(RegistrationFactory):'
         sub = ZMQStream(sub, loop)
 
         # connect the db
-        self.log.info('Hub using DB backend: %r'%(self.db_class.split()[-1]))
-        # cdir = self.config.Global.cluster_dir
-        self.db = import_item(str(self.db_class))(session=self.session.session,
+        db_class = _db_shortcuts.get(self.db_class.lower(), self.db_class)
+        self.log.info('Hub using DB backend: %r', (db_class.split('.')[-1]))
+        self.db = import_item(str(db_class))(session=self.session.session,
                                             config=self.config, log=self.log)
         time.sleep(.25)
         try:

IPython/parallel/tests/__init__.py

@@ -57,7 +57,7 b' def setup():'
     
     cp = TestProcessLauncher()
     cp.cmd_and_args = ipcontroller_cmd_argv + \
-                ['--profile=iptest', '--log-level=50', '--ping=250']
+                ['--profile=iptest', '--log-level=50', '--ping=250', '--dictdb']
     cp.start()
     launchers.append(cp)
     tic = time.time()