DEPRECATED: Paged record topics
A topic that maintains server-side state as a number of lines of record data. The schema defines the record metadata that defines the lines. A client can view the data as pages made up of one or more lines and can page forward and backward through the data.
Paged topics are deprecated. They will be replaced with an equivalent capability in a future release.
It can be simpler to use a JSON topic with delta updates enabled. Although the whole value is published to a client when it first subscribes, subsequent updates are published incrementally.
Paged topics have state which is stored in a tabular format, as pages of lines. Unlike publishing topics, clients do not publish updates to a paged topic to change the state. Instead clients add, update, or remove lines in the topic.
Paged topics can be ordered or unordered. You can define the ordering of a paged topic by using a user-defined comparator class that is located on the Diffusion™ server or by declaring the rules that are used for the ordering when you create the topic. Lines that are added to unordered paged topics are added at the end. Lines that are added to ordered paged topics are added at the position defined by the comparator or rules.
A client must subscribe to a paged topic to be able to access the data on it. However, unlike publishing topics clients do not receive updates whenever changes are made to the paged topic state. To access the data, the client must open a view on the paged topic and specify how many lines per page and what page to open the view on. The client can then page through the data. If the state of the client's current page changes, the client is notified and can choose to refresh the page.
Why use a paged record topic?
Unlike most publishing topics, paged topics are not designed to distribute streaming data. Paged topics store tabular data. If your data is of a more tabular form — for example, news items — a paged topic might be most appropriate.
A paged record topic, enables you to use metadata to define the format of each line of data. If each line contains multiple items of data, paged record topics enables you structure this data, where a paged string topic does not.
The state of publishing topics is constantly changing, with no capability to look back at its previous values. With a paged topic you can store all updates on the topic and a client can view the history of previous values, without the client having to store them.
A paged topic can serve different parts of its state to different clients. Any subscribed client can view any page of the data that is required.
If the order of your data is important, a paged record topic ensures that updates are added in the appropriate position. This removes the requirement for a client to have to order the stored data before using or displaying it.
Considerations when using a paged record topic
Viewing paged topics is supported only by the Classic API.
You must be subscribed to a paged topic to open a view on it.
The lines of a paged topic are UTF-8 encoded.
You cannot use topic replication to replicate paged topics between Diffusion servers.