Publishing data
Consider the following information when deciding how to publish data to topics.
Data type
The updates that you publish to a topic must have a data type and format that matches the data type of the topic.
For example, if your topic is a single value topic where the data is of type integer, all updates published to the topic must contain a single piece of integer data.
Similarly, if your topic is a record topic with a metadata structure defined, all updates published to the topic must have the same metadata structure.
Update size
When considering the format of your data, be aware that the maximum size for a topic update or a message sent through Diffusion™ Cloud is 1 MiB.
Updaters
- Value updater
- This is the preferred type of updater to use with JSON and binary topics. When used as exclusive updaters, value updaters cache the values they use to update topics. This enables them to calculate and send deltas, reducing the volume of data sent to Diffusion Cloud.
- Standard updater
- This type of updater updates topics that use content to represent their data values. Updaters do not cache values and send all of the data passed to them to Diffusion Cloud without performing any optimization.
For more information, see Updaters.
Exclusive updating
To update a topic exclusively, a client registers as the update source for that topic. Only one client can be the active update source for a topic and any attempts by other clients to update that topic fail.
Implementing exclusive updating is more complex than non-exclusive updating as it involves the extra step of registering as an update source.
A single client acting as the exclusive updater can be an advantage if you require that a single client has ownership of a topic or branch of the topic tree. This requires less coordination and management than updating a single topic from multiple clients.
If the ordering of the updates is important, use exclusive updating to ensure that a single client has control over what data is published and when.
If you are using high-availability topic replication, clients must update the replicated topics exclusively. Non-exclusive updates are not replicated by high-availability topic replication.
Non-exclusive updating
To update a topic non-exclusively, a client publishes updates to the topic and, if no other client has registered to update the topic exclusively, the update is applied to the topic.
Non-exclusive updating is the simpler way to update a topic.
Clients that update a topic non-exclusively risk their updates being overwritten by updates from other clients or that updates from multiple clients are published in a different order than intended.
If you use a value updater non-exclusively, the updater does not cache the value used to update the topic.
Non-exclusive updating is not supported with topics that are replicated using the high-availability capability.
Dynamically adding topics
A publishing client can create topics dynamically as and when the topics are required. For example, in response to a subscription request from another client for a non-existent topic.
Security
To publish data to a topic, a client must have the permission for that topic.
For more information, see Permissions.
This page last modified: 2019/11/22