Oracle Database 11 g - Online Public Access Catalog

CHAPTER 8 ■ ORACLE STREAMS 345When you execute the analyze_current_performance procedure, you should run it morethan once in the same session, especially if you are looking for rate, bandwidth, and event andflow control statistics. If you are looking for just the number of current messages in a queue, asingle execution will provide you with this information.Also, your goal is to keep the Streams topology statistics current. You should reexecute thisprocedure when any components are added to any database in the Streams environment.■Note Synchronous capture and messaging client information is not gathered by the DBMS_STREAMS_ADVISOR_ADM package.Streams TopologyWhat makes up the Streams topology? It is composed of databases in the Streams configuration,the Streams components for each database, and the flow of messages between the components.In the Streams topology, messages flow from one component to another component. This isreferred to as a stream path. A path can be something as simple as a capture or synchronouscapture process or an application enqueueing messages into a queue. Another path can be whenthe apply process dequeues the messages. A message will go through several paths queues andpropagations before it reaches the apply process. The stream path ends when messages aredequeued by the apply process.■Note As of Oracle Database 11g Release 1, Oracle Streams does not track paths when messages aredequeued by a messaging client by an application.The Streams path begins from the capture process and ends with the apply process. Alongthe way, there can be multiple source/destinations before reaching the final apply processdestination. The Streams topology assigns a number to each path. This allows for easy monitoringof the paths and location of messages along the path. The Streams topology also designatesa number to a link between two components in a path, the beginning component and an endcomponent. The positions of the link in the overall Streams path can resemble what is listedhere:1. The beginning component is the capture process, and the end component is the queue.2. The beginning component is the queue, and the end component is the propagation sender.3. The beginning component is the propagation sender, and the end component is thepropagation receiver.4. The beginning component is the propagation receiver, and the end component isthe queue.5. The beginning component is the queue, and the end component is the apply.