[cx01]

The author is wrong. Distributed transactions are possible, for example using the Paxos algorithm. In Paxos, if the network fails, the system will block (i.e. become unavailable) until connectivity is restored. It's not possible for one node to commit and the other node to abort.

There is even a paper about using Paxos specifically for distributed commit: http://research.microsoft.com/apps/pubs/default.aspx?id=6463...

[cassandravoiton]

You, sorry to say, utterly incorrect. The Paxos algorithm offers a clever way to making the choise of a single transactional arbitrator dynamic. For each transaction, it might be different, but for a single transcation, Paxos is only stable if the transactional co-ordinator is stable. if the network fails then an unknow state can be achieved and the entire system will have to restabalize to the values held in the single co-ordinator for the broken transaction.

[cx01]

Did you even read the Paxos Commit paper? There is no single arbitrator. And what is 'unknown state' intended to mean? The system will obviously always be in a known state. It will just block as long as there is no network connectivity.

[cassandravoiton]

Yes, I did read it... "

In practice, it is not di±cult to construct an algorithm that, except dur- ing rare periods of network instability, selects a suitable unique leader among a majority of nonfaulty acceptors. Transient failure of the leader-selection algorithm is harmless, violating neither safety nor eventual progress. One algorithm for leader selection is presented by Aguilera et al. [1] "

" The algorithm satisfies Stability because once an RM receives a decision from a leader, it never changes its view of what value has been chosen "

Fundamentally, the idea is that the leader is the transactional arbitrator using the RM as the recorder of that transaction.