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List:       linux-ha-dev
Subject:    Re: [Fwd: Re: [Linux-ha-dev] Re: Thinking about cluster communication
From:       Alan Robertson <alanr () unix ! sh>
Date:       2003-07-29 21:12:12
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Lars Marowsky-Bree wrote:
> On 2003-07-29T08:31:46,
>    Alan Robertson <alanr@unix.sh> said:
> 
> 
>>Forgot to CC this one to the -dev mailing list too...
> 
> 
> Which one? ;-)
> 
> 
>>I think that the issue is *sending* a packet with the expectation of it 
>>being ordered.  Since you'll need a new (additional) sequence number for 
>>this packet type, I see no reason why the interface can't simply be
>>		sendorderedmsg()
>>and maybe	sendclusterorderedmsg() too...
>>
>>And that is the only change.  Ordered packets are delivered in order (but 
>>not total order).  Unordered packets are delivered whenever - with no 
>>relationship to ordered packets.  I believe this is necessary and 
>>sufficient...
> 
> 
> I'd suggest simply serializing the messages which require this property.

I believe that's what I said...

> 
> My idea was to have a 'Concensus Cluster Vote' which elects one of the
> cluster nodes to be the leader for a given service. (Fortunately, given
> that Ram's CCM is returning the membership globally ordered, that's
> reasonably easy and one only needs to do a broadcast & ACK step to make
> sure all nodes agree.)
> 
> Then, the message goes unicast to the leader and that one sends it out
> via the usual heartbeat broadcast mechanism.
> 
> Of course, the cases of leader / node failure need to be covered, but
> even that remains reasonably easy.
> 
> That's not exactly high performance, but the easy way out and yields
> full virtual synchronity.

Good thought.  But, that's not what we're trying to do here...




-- 
     Alan Robertson <alanr@unix.sh>

"Openness is the foundation and preservative of friendship...  Let me claim 
from you at all times your undisguised opinions." - William Wilberforce

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