DDS11 — R#178) Unclear behavior of coherent changes when communication interrupted

The Publisher entity has operations begin_coherent_changes and end_coherent_changes that allow groups of updates to be received by subscriptions as if they were a single update. Although the specification already contains a general statement about receivers not making updates available until all have been received, no specific mention of communication interruptions or configuration changes is made. This omission has caused questions to be raised with regards to the interactions between coherent changes and partitions, late-joining DataReaders, and network failures.

Proposed Resolution:

The specification should be amended to state that a Publisher should not prevent users from changing its partitions while it is in the middle of publishing a set of coherent changes, as the effect of doing so is no different than that of any other connectivity change. However, in the event that connectivity changes occur between the publishers and receivers of data such that some receiver is not able to obtain the entire set, that receiver must act as if it had received none of the data.

Proposed Revised Text:

Append the following text to the second paragraph of section 2.1.2.4.1.10 begin_coherent_changes:

A connectivity change may occur in the middle of a set of coherent changes; for example, the set of partitions used by the Publisher or one of its Subscribers may change, a late-joining DataReader may appear on the network, or a communication failure may occur. In the event that such a change prevents an entity from receiving the entire set of coherent changes, that entity must behave as if it had received none of the set.

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