Consumers

Consumers are applications that you create such as analytics applications, reporting tools, or enterprise dashboards.

They use the MapR Event Store For Apache Kafka APIs to request messages from topics that they are interested in. In case of server failure, consumer clients continually retry requests automatically. A consumer client library sends unread messages, which consumers extract data from.

Consumers can run as separate processes on a single machine and as processes on different machines.

Before a consumer can read messages from topics, the user ID running the consumer needs these permissions:
  • The readAce permission on the volume where the streams are located. For information about how to set permissions on volumes, see Setting Whole Volume ACEs.
  • The consumeperm permission on the streams where the topics are located. Users with the adminperm permission on those streams can grant the consumeperm permission.

Subscriptions

Consumers subscribe to topics. When a consumer subscribes to a topic or partition, it means that the consumer wants to receive messages from that topic or partition. For example, an analytics application might subscribe to the topics rfids_productA, rfids_productB, and more to track movement of products from factories to distribution centers. A reporting tool might subscribe to the topics meters_NW, meters_SW, and more to get a report of electricity usage in different geographic regions that a power company services.

A subscription is the list of the topics that a consumer is subscribed to.