[Ocfs2-devel] ocfs2_controld.cman

[David Teigland]

On Thu, Apr 09, 2009 at 01:38:10PM +0200, Andrew Beekhof wrote:
> On Thu, Apr 9, 2009 at 00:22, Joel Becker <Joel.Becker at oracle.com> wrote:
> >
> > ? ? ? ?Well, this is going to be fun. ?I have to figure out which
> > daemon is the "first", and now it's just racy. ?I could swear that
> > someone told me cpg would guarantee i see the joins in order, not at the
> > same time.
> 
> "In order" does not necessarily imply "one node at a time".
> 
> I don't consider it unreasonable for two nodes starting (effectively)
> simultaneously to appear in the first membership.
> I believe Heartbeat had the same property.

Right, confchg order is guaranteed, but doesn't imply one node per confchg.

> Why not just take a lock when you want to create the daemon_protocol
> section (and allow the second guy to fail gracefully)?
> Perhaps cpg even has something like this built in...

You probably want to use cpg messages to order things.  So, for example,
everyone sends a message proposing that it create the section, and the node
whose message arrives first does it.  If you're coordinating things with
messages like this anyway, it's not much more work to include protocol
information in the message and eliminate checkpoints.

Dave