Sun Microsystems iPlanet Integration Server 3.0, Process System Manual

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Monitoring and Changing Engine States
Chapter 4 Managing Engines 123
3.
Click the Set Primary button in the Engine Status window. The primary unit
now becomes the backup unit, and the backup becomes the online unit.
About Recovering State Information
In a production system, placing a backup unit online requires recovering state
information from the engine database. State information includes the state of every
process instance, the state of every activity and timer within each process instance,
the values of process attributes and their lock states, the state of routers and
triggers for each activity instance, session activity lists, queue lists, and so on.
Accordingly, recovery of state information is not instantaneous. It takes an amount
of time proportional to the amount of state information in the engine database, and
inversely proportional to the speed of database access. The amount of state
information available for a given process instance is determined by the process
recovery level specified in the process definition or by the client application.
The recovery level is really a performance parameter that specifies how much state
information about a process instance is stored persistently in the engine database.
The less state information stored in the database, the higher the level of engine
performance in executing that process instance, but the lower the level of recovery
possible when a backup engine unit comes on line.
Recovery levels are specified on a per process basis (not per engine). There are
three options.
None No state information is written to the engine database so none can be
recovered—the process instance is therefore terminated when an engine fails and a
backup unit comes on line.
Process only Minimal information is written to the engine database—only
enough to recreate the process instance from its start. When an engine fails and a
backup unit comes on line, all state information is lost and the process instance is
recreated from start and executed anew.
Full recovery All state information for a process instance is written to the engine
database. When an engine fails and a backup unit comes on line, state information
is recovered as needed to proceed with process execution, that is, to evaluate
assignment rules, change an activity state, and so on.
NOTE Writing of data to the engine database also depends on the logging
properties of the engine configuration (see
“How to Configure a
New Engine” on page 95 ).