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Each resource that SSM controls is represented by a row in a resource table. This row contains information about the resource, such as its current and desired states, the resource name, and the names of its prerequisite resources. Information on the current and desired states of a resource is maintained in the CURRENT_STATE and DESIRED_STATE columns respectively. An AOF message rule usually updates the CURRENT_STATE column; however, in some cases, such as during startup, it may be updated by other programs. Either a CMD rule or the Schedule Manager usually updates the DESIRED_STATE column. Both the DESIRED_STATE and CURRENT_STATE columns are monitored columns; therefore, if a change is made to either one, then the RDF posts the SSM engine to run.
When the SSM engine is posted to run, it compares the desired state of all resources to their current state and checks to see whether any missing prerequisites have been satisfied. If the current or desired state of a resource has changed, and the current state does not equal the desired state, then the SSM engine dispatches an action. The action is taken from the action text column of an action table.
In addition to scanning the resource tables when a change occurs, the SSM engine also scans all resource states every nnnn seconds, based on the value you set in the STATEMAXWAIT parameter. For more information about this parameter, see the chapter “Parameters for Facilities” in the Parameter Reference.
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