iIS Process Engine Components
32 iPlanet Integration Server • P rocess System Guide • August 2001
Figure 1-2 Minimal Engine Configuration
Engine Unit The engine unit is an application that performs all the basic iIS
engine functions (see “What Does an iIS Process Engine Do?” on page 36). The
engine unit is a single iPlanet UDS server partition containing a number of
manager objects (see Figure1-5 on page 37). The engine unit, in performing its
work, tracks the state of each process, activity, timer, process attribute lock, and
session that it creates in the course of process execution. In a typical production
situation, the engine unit maintains state information on tens of thousands to
millions of objects. It is critical that this state information be kept in a persistent
form should the engine unit fail and need to be recovered. For this reason, the
engine unit writes all current state information to the engine database (described
below).
Database Service The database service is an application that manages the engine
unit’s database access. The database service is a single iPlanet UDS server partition
that maintains communication channels with the engine unit, opens a session with
the engine database, and writes and retrieves state information as required by the
engine unit. The database service is a single–threaded application, and can handle
only one request to the database at a time. (To see how to overcome this limitation,
see “Full Configuration: Failover and Load Balancing Combined” on page 35.)
Engine Database The engine database provides persistent storage for state
information maintained by the engine. It also stores registration information
regarding all process definitions, assignment rule libraries, user profiles, and
validations that can be executed by the engine. In addition, the engine database can
be used to log historical information for tracking process execution over time. The
iIS Process Engine
Client Applications
Primary
Engine
Unit
Engine
Database
Database
Service