As implemented in the Metasys system, RabbitMQ is the message bus which supports features such as trending data, Site Management Portal UI and Metasys UI navigation tree features. The Site Director maintains a queue that receives messages which are then processed. These messages notify users of changes from other system devices, system health, trends, and alarms. When the Site Director is busy, the messages remain in the queue until the Site Director is available to process them. Using RabbitMQ allows the system to avoid bottlenecks by separating the actions of receiving and processing data. All message queuing functions happen within the server itself; no messages from RabbitMQ broadcast over the network between the server and other devices.
Metasys installs RabbitMQ on all computers where ADS, ADX, or OAS software is installed. After you install RabbitMQ, do not stop, disable, or uninstall it. If you stop, disable, or uninstall RabbitMQ, the Site Director does not receive or process messages. This can lead to an irrecoverable loss of trending data. You can also lose messages about Alarms, Audits, Online Archive Updates, Destination Delivery Agent, and Scheduled Reports. The queue fills at a rate determined by your site configuration and system use; for example, trend frequency or number of additions, changes, or deletions made to the navigation tree.
An alarm is generated in the Metasys system when any trend or alarm sample remains in the RabbitMQ for more than 10 minutes. This alarm usually indicates a problem with Microsoft SQL Server® or a remote forwarding destination is offline.
An alarm is generated in the Metasys system when trend samples remain in the queue after failing two bulk inserts. If this scenario occurs, trend samples go into a single insert mode. An alarm is generated for each trend sample that falls back to a single insert mode. JavaScript Object Notation (JSON) files are created for each trend object that has a sample that cannot be processed. The JSON files are located in the JCIHistorian database.