using virtual synchrony for CTDB

Tracy Camp campt at
Fri Oct 6 18:09:54 GMT 2006

Snake oil aside, 'DLM' like clustering schemes, which the CTDB proposal 
seems like it could be grouped with, are best implemented with p-t-p 
messages for the latency concerns already expressed.  However also using a 
VS group communications layer to provide a generation number than can then 
be embedded in each P-T-P message provides P-T-P w/o the overhead of VS 
for the latecy sensitive messages.  Sort of a scheme that breaks the 
'control' apart from the 'data' transports.

Tracy Camp

On Fri, 6 Oct 2006, David Boreham wrote:

> Steven Dake wrote:
>> I have a suggestion to use virtual synchrony for the transport mechanism
>> of CTDB.  I think you will find using something like TCPIP unsuitable
>> for a variety of reasons.
> I'm very far from being a VS expert, but when I looked into a few
> of the open source implementations available a while back it became
> clear (to me at least) that they have a kind of 'snake oil' property
> in that they appear to deliver magical services but do so only by
> using quite inefficient methods underneath the covers. For example
> it appears that one is avoiding network round-trips but in fact to implement 
> its
> delivery guarantees the message middleware layer needs to propagate a token
> around the set of participating nodes which of course involves many sends and
> receives.

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