RTI Persistence Service
Persistence Service is a Connext DDS application that is configured to persist topic data. Persistence Service is included with the Connext DDS Professional, Evaluation, and Basic package types. For each one of the topics that must be persisted for a specific domain, the service will create a DataWriter (known as PRSTDataWriter) and a DataReader (known as PRSTDataReader). The samples received by the PRSTDataReaders will be published by the corresponding PRSTDataWriters to be available for late-joining DataReaders.
For more information on Persistence Service, please see:
- Introduction to RTI Persistence Service
- Configuring Persistence Service
- Running RTI Persistence Service
Persistence Service can be configured to operate in PERSISTENT or TRANSIENT mode:
- TRANSIENT mode The PRSTDataReaders and PRSTDataWriters will be created with TRANSIENT durability and Persistence Service will keep the received samples in memory. Samples published by a TRANSIENT DataWriter will survive the DataWriter lifecycle but will not survive the lifecycle of Persistence Service (unless you are running multiple copies).
- PERSISTENT mode The PRSTDataWriters and PRSTDataReaders will be created with PERSISTENT durability and Persistence Service will store the received samples in files or in an external relational database. Samples published by a PERSISTENT DataWriter will survive the DataWriter lifecycle as well as any restarts of Persistence Service.
Peer-to-Peer Communication:
By default, a PERSISTENT/TRANSIENT DataReader will receive samples directly from the original DataWriter if it is still alive. In this scenario, the DataReader may also receive the same samples from Persistence Service. Duplicates will be discarded at the middleware level. This Peer-To-Peer communication pattern is illustrated in Figure 6. To use this peer-to-peer communication pattern, set the direct_communication field in the DURABILITY QosPolicy to TRUE. A PERSISTENT/TRANSIENT DataReader will receive information directly from PERSISTENT/TRANSIENT DataWriters.
Figure 6 Peer-to-Peer Communication
Relay Communication
A PERSISTENT/TRANSIENT DataReader may also be configured to not receive samples from the original DataWriter. In this case the traffic is relayed by Persistence Service. This ‘relay communication’ pattern is illustrated in Figure 7. To use relay communication, set the direct_communication field in the DURABILITY QosPolicy to FALSE. A PERSISTENT/TRANSIENT DataReader will receive all the information from Persistence Service.
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