6. Partition merge occurs
Ok.
7. SFBS state on nodes of second group is rewriten by state of first unfished group
No. Here, you make the assumption that you can have CONCURRENT access to the
SAME SFSB which is not allowed per spec.
Maybe that's one of the points. As I understand partion "split" each groups things that all nodes in other group are down, but they are not so there is not chance how to avoid concurrent access.
Anyway the same problem can occur in DistributedState service from JBoss Clustering framework, where no such limitaton is explicitly given by spec.
Furthermore, even in the strange scenario you describe (concurrent access to a same SFSB), the merge would not update the remote nodes until a new SFSB operation occurs i.e. with SFSB, we replicate only when we modify a SFSB, not when a merge occurs.
That's even worst.
Suppose after partition merge group 1. has SFSB in state A and group 2. has SFSB in state B.
First, as I belive, after partition merge you can get inconstent behavior. If you use SFSB replica from node in group 1. you get state A if you read SFSB replica from node in group 2. you get state B.
Second, when SFSB modify to state C occurs, one node rewrites state B and A on all other nodes. So group of nodes went through states A-C and group through states A-B-C with all consequences.
Maybe I could try to prepare some testcase demonstrating problem.
Sorry if am I missing something, but I still strongly believe, that merging partions is very dangerous and can put cluster in inconsistent state. It seems to me, that it is as complicated as to try "merge" the state of two computers (processors, memory, I/O devices) after they run separateted for a while.
Anyway, beside my complains, jboss clustering is really great, thank you for this great job.
David
8. Cluster finishes computation again and changes SFBS state and produces output (assigns AGAIN money to account)
So we get as I belive incorrect and dangerous cluster behavior.
Do we agree now?
Cheers,
Sacha
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