Sample

A sample is the unit of data exchanged between DataStorm publishers and subscribers. It provides multiple data members that can be accessed using getter methods. Each sample has three template parameters — Key, Value, and UpdateTag — which are specified when a topic is created. All samples published to a topic must use the same Key, Value, and UpdateTag types defined by that topic.

Members

Key

The key organizes the samples published to a topic. Readers can use keys to filter which samples they want to receive, and writers can use keys to identify the source or category of the data. You can access the key with the sample’s getKey method.

Value

The value is the application-domain data that writers publish and readers receive. It can be accessed using the sample’s getValue method.

If no value is available (for example, if the event is Remove), getValue returns a default-constructed value. You should check the sample’s event type before calling getValue() to ensure the sample actually contains a value.

Event

The event identifies the type of the sample and communicates lifecycle operations to subscribers. It can be obtained using the getEvent method, which returns a SampleEvent enumerator:

• Add — indicates a new value is being published.

• Update — indicates that an existing value has changed.

• Remove — indicates that the value has been removed and no value is included in the sample.

• PartialUpdate — indicates that the sample contains a partial update to the value.

For Remove samples, the value is a default-constructed instance. For PartialUpdate samples, the sample also provides the update tag, which can be retrieved using getUpdateTag().

The value returned by getValue for a PartialUpdate event is the result of applying the updater associated with the tag returned by getUpdateTag. If no updater is registered for this tag, the partial update is ignored and the current value remains unchanged.

Timestamp

The timestamp represents the time at which the sample was written. It is set by the writer when the sample is sent and can be obtained with the getTimestamp method, which returns astd::chrono::time_point<std::chrono::system_clock> value.

Timestamps are expressed in UTC and are independent of the system’s local time zone, making them suitable for exchanging data between machines with different regional settings.

Origin

The origin identifies the writer that created the sample. It can be obtained using the getOrigin method. The origin corresponds to the name of the writer that published the sample.

Session

The session identifies the connection between the two nodes that exchanged the sample. It can be obtained with the getSession method. This session identifier can be passed to Node::getSessionConnection to retrieve the corresponding connection between the two nodes.