[jgroups-users] Protocols' questions

Hello,

I am trying to make my mind up regarding some of the protocols JGroups provides - I don't have a lot of experience with it  therefore forgive me if some questions
are blatantly naïve - I did read the docs a few times but I am still unsure.

It seems to me that many of the protocols have an UDP "mindset", namely they make most sense when used upon UDP as transport protocol, I am debugging an issue
Whose jgroups' stack involve the following (more or less):

<FRAG>
<STABLE>
<NACK2>
<UNICAST2>
<TCP>

I am investigating if I could simplify it and I few questions popped up

Reading the <UNICAST2> documentation:

>On top of a reliable transport, such as TCP, UNICAST is not really needed. However, concurrent delivery of messages from the same sender is prevented by UNICAST by acquiring a lock on the >sender's retransmission table, so unless concurrent delivery is desired,

What is it actually meant by "concurrent delivery" ?

Does it refer to the fact that JChannel.send() is not synchronized therefore, when sending an bunch messages we could end up with a catastrophic
mess where bits of messages get scattered on the stream and the whole thing becomes un-intelligible to the receiver ?

Does it make sense to have one among UNICAST{1,2,3} and NACKAK{1,2} in the stack ? Wouldn't that be redundant ?

Does STABLE make sense if we are using TCP to deliver messages to the cluster's members ?

Does FRAG make sense if, by using a connection-oriented protocol such as TCP, we don't have a max datagram size to stick to ?

Thanks,
Pietro



Pietro Paolini
Consultant

Alfa
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