23.4. Ordering message delivery

We have seen that a group of processes may be set up and may execute distributed algorithms. Each member may be maintaining a data replica and we have seen how a single update may be committed by all members of the group or by none of them, using quorum assembly followed by an atomic commitment protocol. Concurrent update requests are serialized by the fact that only one quorum assembly can succeed. Strong consistency has been achieved, we have single copy serializability and have imposed a total order of updates system-wide (within the group).

In the above we did not take into account the order in which the update requests originated. We could specify an additional requirement: that updates are committed at the ...

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