[sheepdog] [PATCH] sheep: remove master node

[MORITA Kazutaka]

At Thu, 18 Jul 2013 16:45:40 +0800,
Liu Yuan wrote:
> 
> > > I noticed zookeeper just send one event to watcher on my test box even if there
> > > are multiple updater to one member of the queue. But I think there is problem
> > > like above example. I think we need to check if there someone updates the join
> > > event already in the queue inside push_join_response(), to allow only one
> > > updater thus one update event to watcher of all nodes.
> > 
> > It is not easy to make sure that there is only one updater in the
> > cluster.  I think of keeping the master of the zookeeper driver in
> > this patch.  This patch cannot remove the master in either way, and
> > introduces another complexity rather than simplifying the code.
> > 
> 
> Why hard? We can read the zk node and check ev->type == EVENT_ACCEPT or not. no?

While pushing a join response, how to prevent another node from
updating the same zk node?  For example,

 1. The node A reads the znode and ev->type is not EVENT_ACCEPT.
 2. The node B reads the znode before the node A updates it with
    EVENT_ACCEPT.
 3. The node A calls zk_set_data() with EVENT_ACCEPT.
 4. The node B calls zk_set_data() with EVENT_ACCEPT.

Thanks,

Kazutaka