Chapter 1 -
Overview of Oracle Job Scheduling
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are no scheduled tasks present in the system.
Since some of the external schedulers available
on the most common operating systems have been presented, the
following section will focus on the internal schedulers provided by
the Oracle database.
Internal Oracle Job Scheduling
The Oracle scheduler allows jobs to be
scheduled to run at a later date, or on a repeating cycle.
Information about the scheduling session’s environment is stored
along with the scheduled job, allowing jobs to run in a consistent
environment each time. Scheduled jobs are placed on a job queue
that is managed by a coordinator process, which periodically scans
the job queue looking for jobs to execute. When necessary, the
coordinator process spawns job slaves to execute the jobs. The
basic architecture of the Oracle scheduler is shown in Figure 1.10.
Figure 1.10 – Oracle Scheduler Architecture
The basic architecture of Oracle 9i and Oracle
10g schedulers may be similar, but the functionality and associated
APIs are quite different. The Oracle 9i scheduler is extremely
basic and a little clumsy, while the Oracle 10g scheduler is packed
with features allowing job scheduling to be as simple or complicated
as desired. The original scheduler API has been retained in Oracle
10g for backwards compatibility, and it is this scheduler that will
be focused on first.
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