Re: [jgroups-dev] How to implement/use flow control in JGroups

Mike Jensen wrote:
> I think I found a good solution here. Let me know if you see any
> problems with this.
>
> I have set it up to use TCP, and removed the FC protocol. I then
> configured TCP to not use the send queue. It seems that this allows us
> to block (I assume from the kernel level from a quick inspection). I
> then just added a thread pool to handle calling back to alert we are
> ready to send more. Any worries about this setup?

This probably works.

> I tried to remove STABLE and NAKACK. As I did not understand a need for
> these with the use of TCP (unless a server goes down, in which case I am
> not concerned). But I continue to get warnings where it says
> digest=null.

NAKACK maintains vectors of seqnos received and delivered for every 
member, e.g. 4:22:1:0:442. These are updated when a message is received 
and are used to prevent duplicates and for retransmission of missing 
messages. A new member needs to get the latest up-to-date vector, so 
it'll know that the next message from P to be expected is 42 (for example).

Therefore GMS has a dependency on NAKACK; the stack won't start if you 
remove NAKACK.

STABLE is also needed to purge (stable) messages seen by everyone.



-- 
Bela Ban
Lead JGroups / Clustering Team
JBoss

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