- By default, delta streaming is enabled.
If this property is set to true, delta streaming is disabled and
all values are published in full.
If there is little or no relationship between one value published to a topic and the next,
delta streams will not reduce the amount of data transmitted. For such topics, it is
better to set PUBLISH_VALUES_ONLY.
- If set to true, the latest value of the topic is not retained by
the Diffusion™ server or the client that publishes it.
New clients that
subscribe do not receive an initial value. No value will be returned for fetch operations that select the topic.
For time series topics, if DONT_RETAIN_VALUE is set to true,
time series events are still retained, but the latest value is not stored separately.
The DONT_RETAIN_VALUE property is useful for applications like a
feed of news items, or for values that are only valid at the moment of publication.
You can combine this with VALIDATE_VALUES.
Using DONT_RETAIN_VALUE reduces the topic memory footprint, but disables delta streaming.
Disabling delta streaming is likely to increase the bandwidth used unless subsequent values are unrelated.
This property replaces the deprecated stateless topic type which sends untyped byte data and requires clients to
interpret and validate the data.
- The path to the topic that acts as the master topic to a slave topic.
A topic is not required to exist at this path at the time the slave topic is
- If set to true, when a session unsubscribes from
the topic, any updates for the topic that are still queued for the session are
There is a performance overhead to using this option as the client queue must be
scanned to find topic updates to remove, however it may prove useful for preventing
unwanted data being sent to sessions. This property is disabled by default.
- Set this to the type name of a Diffusion
data type. All events in the time series are of this data type. The type name can be
one of the following values:
- Set this to a range expression that specifies the range of events
retained by a time series topic. When a new event is added to the time series, older
events that fall outside of the range are discarded. If the property is not specified,
a time series topic retains the ten most recent events.
For more information about
range expressions, see Range expressions.
- Set this to a range expression that specifies the range of
events sent to all new subscribers.
If a range expression is specified for this
property, the specified subscription range is sent to the client session. This is
true whether delta streams are enabled for the topic or not. However, to receive all
the events in the specified range, the subscribing client session must register a
stream before it subscribes to the topic. If a stream is not registered before
subscription, the session receives only the latest value.
If the property is not specified, new subscribers will be sent the latest event if
delta streams are enabled for the topic and no events if delta streams are disabled
for the topic.
For more information about range expressions, see Range expressions.
- If set to true, the topic rejects updates that would
create invalid instances of the topic's data type.
If set to anything other than
true, no validation is performed and all values are streamed to
subscribing clients whether they are valid data or not.
Validation has a performance overhead and is disabled by default.
Note: If validation is disabled and the value provided is not valid, the client might
produce errors or other unexpected behavior. The exact error varies depending on the
client platform. To avoid this, use the client-side validation method provided by
the Diffusion API.
- Optionally, define valid records and fields of a recordV2 topic.
A recordV2 topic contains records, which can be divided
into fields. The schema names the records and fields and provides a mechanism for
direct access to the fields. The schema is also used to validate the data to ensure
it complies with the schema definition. The schema property is supplied as a JSON
string that can be generated from a Schema object.
If no schema is provided, the topic data can be free format.