Streams Clients and Event Flow

The Streams clients are controlled by rules. A rule is a database object that enables a Streams client, such as Capture, Apply, or Propagation, to perform an action when an event occurs and a condition is satisfied.

All about Queues

Queues are an important component in the Streams Infrastructure.  Streams processes use queues to stage events in preparation for sending them to the remote database by Propagation or consumption. Propagations send events from one queue to another.  These queues can be in the same database or in different databases.

The queue from which the events are propagated is called the source queue, and the queue that receives the events is called the destination queue. Typically, the source queue stays in the source database, and the destination queue will be in the remote database. In terms of sending the messages, there can be a one-to-many, many-to-one, or many-to-many relationship between source and destination queues. It is more like a transfer to another staging area for further use. Events that are staged in a queue can be consumed by an Apply process, a messaging client, or by an application.

Messages are propagated between a source queue and a destination queue.  Although Propagation always occurs between two queues, a single queue may participate in multiple Propagations. That is, a single source queue may propagate events to multiple destination queues, and a single destination queue may receive events from multiple source queues. However, only one Propagation is allowed between a particular source queue and a particular destination queue. A single queue may also be a destination queue for some propagations and a source queue for other propagations.