DDSI-Specific Transient-Local Behaviour

The DCPS specification provides transient-local, transient, and persistent data. The DDSI specification only provides transient-local, which is the only form of durable data available when inter-operating across vendors.

In DDSI, transient-local data is implemented using the Writer History Cache (WHC) that is normally used for reliable communication. For transient-local data, samples are retained even when all Readers have acknowledged them. The default history setting of KEEP_LAST with history_depth = 1, means that late-joining Readers can still obtain the latest sample for each existing instance.

When the DCPS Writer is deleted (or is unavailable), the DDSI Writer and its history are also lost. For this reason, transient data is typically preferred over transient-local data.

Note

Eclipse Cyclone DDS has a facility for retrieving transient data from a suitably configured OpenSplice node, but does not include a native service for managing transient data.