Partitions

Concept

The Partition QoS provides another way to control which DataWriters will match—and thus communicate with—which DataReaders. It can be used to prevent DataWriters and DataReaders that would have otherwise matched with the same Topic and compatible QosPolicies from talking to each other. Much in the same way that only applications within the same domain will communicate with each other, only DataWriters and DataReaders that belong to the same partition can talk to each other.

The Partition QoS consists of a set of partition names that identify the partitions of which the Entity is a member. These names are simply strings, and DataWriters and DataReaders are considered to be in the same partition if they have more than one partition name in common in the Partition QoS set on their Publishers or Subscribers.

Example Description

In the Publisher application, we change the Partition name list every 5 samples. Our purpose is to show how literals and regular expressions can be used to match the subscriber's name list.

In the subscriber application, we create a reliable reader, and request old samples upon joining, showing that partitions are subscriber-based, not data-based. If we start the subscriber late, it will receive all samples available, even those that were published while under incompatible partitions.

Furthermore, if the reader and writer unpair due to a partition mismatch, the reader will interpret the instance as new if it reconnects.

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