Re: [jgroups-dev] Question on FD

On 3/27/12 6:53 PM, Sundararajan, Mukund wrote:
> Thanks for the answer. It helped us. Have an architectural question. We are building a cluster that could contain up to 60 nodes. Our requirements call for TCP to be used as transport instead of multicast or UDP.

That's definitely *not* something I recommend ! If you send a 
'multicast' (= cluster-wide) message to a 60 node cluster, you have to 
send the message 59 times, versus an IP multicast where the datagram 
packet is sent only once.

Also, if everybody sends, you'll have a mesh of ~ 60 x 60 TCP 
connections and (currently, in TCP) 60 threads open (if everybody 
sends), or N threads (1 for each sender) in general.


> I've read the documentation and it suggests there is no need to use UNICAST or UNICAST2 if TCP is the transport.


Where did you see that ? I recommend to take the udp.xml, copy it into a 
tcp.xml, and replace UDP --> TCP and PING --> TCPPING or MPING, plus 
remove a few properties from UDP. Or take tcp.xml (shipped with JGroups) 
as a starting point.

No, UNICAST needs to remain in the config, for ordering reasons. See the 
wiki for details.

> We will be sending point to point messages in the cluster but most of the messaging will be from one sender to all nodes in the cluster.


OK, then it's not so bad as when everybody sends multicast messages.


> Is it sufficient to configure pbcast.NAKACK?
>
> Do we need UNICAST or UNICAST2 in addition to pbcast.NAKACK?


If you use a 3.1.x release, I recommend UNICAST2 and NAKACK2. If you use 
3.x, I recommend UNICAST2 and NAKACK.


> If we did configure UNICAST, will it have a role to play when a sender is multicasting to all nodes in the cluster or would it come into play only in point 2 point communications between two nodes in the cluster?

UNICAST is only used for point-to-point messages; NAKACK(2) is used for 
point-to-multipoint messages.


-- 
Bela Ban, JGroups lead (http://www.jgroups.org)

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