DistribuSys

DistribuSys (Distributed Systems) is a configuration option that allows multiple systems to share data and control.

The purpose of a distributed project is best illustrated by comparing it to a stand-alone project. In a stand-alone project, the system has a set of records that it controls. The system can:

• Issue commands against a given record.

• Configure the record.

• View record events.

• Receive record alarms.

• Collect historical data from the record.

Applications that run on stand-alone systems work with the data that exists in the system.

In a distributed installation, two or more systems share data and control. All systems can hold non-global data, such as analog, status, rate, and remote tables. Each system contains a RealTime database (RTDB) with a consistent configuration size; however, the databases only contain required records. If a system does not have the privileges for accessing a record, then the record is not distributed to this system. This allows for the creation of small systems requiring less memory and disk space.

The RealTime database (RTDB) in the distributed installation has four types of tables: Local, Global, Distributed, and DOAS Support.

• Local tables are not replicated to other systems within a distributed installation.

• Global Tables exist on each system within a distributed installation.

All records within a global table are common to each system within a distributed installation. Run time additions and changes, although rare, are replicated to all systems in a distributed installation.

• Distributed Tables contain a dataset field that assigns privileges and controls replication between systems.

• DOAS Support Tables describe the DistribuSys configuration for the project. All systems must have identical copies of these tables for distributed project to work properly.

In order to prevent conflicts when multiple systems are capable of acquiring field data, only one system should acquire the data actively (for example, polling the remote). Therefore, only one system should "own" the related records at any given time. The transfer of ownership, as well as other privileges, between systems is accomplished through mode records. Refer to the modes documentation for more information.