Availability Guide for Application Design

Instrumenting an Application for Availability
Availability Guide for Application Design—525637-004
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The Subsystem Programmatic Interface (SPI)
This kind of event might indicate that a disk is getting full or a message queue is
getting full. Or it might result from statistical data indicating, for example, that an
error rate has exceeded some threshold value.
In addition to indicating that a threshold has been crossed, this category of event
messages should also contain:
•
The name of the object
•
The current level of use of that object
•
The previous level of use or direction of travel (that is, rising above or falling
below the threshold)
•
Suggested action, if appropriate
Command Messages
Command messages are SPI messages that allow human or automated operators to
monitor and control objects in the DSM subsystem environment. These messages are
built on behalf of the operator by DSM management applications using SPI
procedures.
To effectively control the objects in an application, your application must support a set
of commands consistent with the management model to be used. These SPI
commands are typically either initiated by the operator or occur in response to event
messages. These commands include state changes, state inquiries, attributes
modifications, and attribute inquiries.
State-change commands allow a human or automated operator to change the state of
an object. State-inquiry commands allow the operator to inquire about the state of an
object. Attributes modifications allow the operator to modify the values of the different
attributes of an object.
Components of Command Messages
A command message contains tokens representing the following:
•
An identification of the subsystem or application that will receive the message
•
The specific command that the application must execute
•
The type of object affected
This element indicates the category of objects to which the target object of the
command belongs; for example a file, a terminal, or an automated teller.
•
The name of the specific object the command applies to
This element indicates which file, terminal, or automated teller is to be affected.
•
Other command information specific to the command