Currently, devstack doesn't support mysql as ceilometer backend, but for now, that is what I do :

1. enable ceilometer in localrc

enable_service ceilometer-acompute,ceilometer-acentral,ceilometer-collector,ceilometer-api

2. change the database connection in lib/ceilometer

iniset $CEILOMETER_CONF database connection mysql://root:rachel@localhost/ceilometer?charset=utf8

where rachel is mysql password for root.

3. change ceilometer/collector/service.py code

    $ git diff
    diff --git a/ceilometer/collector/service.py b/ceilometer/collector/service.py
    index 898e551..91b8c70 100644
    --- a/ceilometer/collector/service.py
    +++ b/ceilometer/collector/service.py
    @@ -112,6 +112,7 @@ class CollectorService(rpc_service.Service):
         def __init__(self, host, topic, manager=None):
             super(CollectorService, self).__init__(host, topic, manager)
             self.storage_conn = storage.get_connection(cfg.CONF)
    +        self.storage_conn.upgrade()

         def start(self):
             super(CollectorService, self).start()

then run ./stack.sh, it will generate mysql db tables during ceilometer-collector starts.