In computer-related technologies, a publish—subscribe model is typically a messaging model where computer-implemented senders of messages, called publishers, publish messages to be consumed by interested computer-implemented receivers, called subscribers. A publisher is an entity that publishes messages. A subscriber is an entity that subscribes to or consumes the subscriptions published by the publisher. A producer is an entity that produces information that is published by the publisher. A publisher may publish messages regardless of a number of subscribers, interests of subscribers etc.
The publishers typically publish messages as a stream of updates and the subscribers consume the messages to which they are subscribed to from the stream of updates. Typically different subscribers have different consumption rates. That is, each of the subscribers in the publish-subscribe system may consume messages at different rates. For example, a first subscriber may consume X number of messages per second and a second subscriber may consume Y messages per second. If a publisher is publishing a total of Z number of messages per second, then the first subscriber may be lagging behind by (Z-X) number of messages and the second subscriber by (Z-Y) number of messages. The publisher may have to refetch the messages that are not consumed by the subscribers from a storage system and publish them again. This may lead to the publisher making excessive calls to the storage system, which consumes a significant amount of time and thus, may introduce further delays in the system.
Further, in certain publish-subscribe systems, if the subscriber fails temporarily and recovers after a brief period or simply does not receive a message, the publisher may not know a point from which the messages may have to be republished to the subscriber.
Additionally, certain publish-subscribe systems may be so tightly coupled that scalability is an issue and routing messages to subscribers at different locations may not be efficient. In current publish-subscribe systems, publishers that publish more than a set of subscriptions to the same subscriber may do so by establishing as many connections with the subscriber as the number of sets of subscriptions. However, establishing too many connections can consume a significant amount of computing, storage, and network resources.
In at least some publish-subscribe systems, a producer who generates information to be published as subscriptions and the publishers may be tightly coupled applications. That is, the producer may be designed to work with a specific publish-subscribe system. Such publish-subscribe systems may not be compatible with producers that may not be designed for a specific publish-subscribe system. This may limit the types of producers whose messages may be published using the publish-subscribe systems and also the types of messages that may be published.
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