Advanced Queuing - Oracle

Propagation Features
Propagation Scheduling
A propagation schedule is defined for a pair of source and destination queues. If a
queue has messages to be propagated to several queues, a schedule has to be
defined for each of the destination queues. A schedule indicates the time frame
during which messages can be propagated from the source queue. This time frame
may depend on a number of factors such as network traffic, load at source database,
load at destination database, and so on. The schedule therefore has to be tailored for
the specific source and destination. When a schedule is created, a job is
automatically submitted to the job_queue facility to handle propagation.
The administrative calls for propagation scheduling provide flexibility for
managing the schedules (see "Scheduling a Queue Propagation" in Chapter 9,
"Administrative Interface"). The duration or propagation window parameter of a
schedule specifies the time frame during which propagation has to take place. If the
duration is unspecified, the time frame is an infinite single window. If a window
has to be repeated periodically, a finite duration is specified along with a next_
time function that defines the periodic interval between successive windows.
The latency parameter for a schedule is relevant only when a queue does not have
any messages to be propagated. This parameter specifies the time interval within
which a queue has to be rechecked for messages. Note that if the latency is less than
5 seconds, then the job_queue_interval parameter for the job queue processes
should be less than or equal to the latency parameter.
The propagation schedules defined for a queue can be changed or dropped at
anytime during the life of the queue. In addition there are calls for temporarily
disabling a schedule (instead of dropping the schedule) and enabling a disabled
schedule. A schedule is active when messages are being propagated in that
schedule. All the administrative calls can be made irrespective of whether the
schedule is active or not. If a schedule is active, it will take a few seconds for the
calls to be executed.
Scenario
In the BooksOnLine example, messages in the OE_bookedorders_que are
propagated to different shipping sites. The following example code illustrates the
various administrative calls available for specifying and managing schedules. It also
shows the calls for enqueuing messages into the source queue and for dequeuing
the messages at the destination site. The catalog view USER_QUEUE_SCHEDULES
provides all information relevant to a schedule (see "Selecting Propagation
Schedules in User Schema" in Chapter 10, "Administrative Interface: Views").
8-108 Oracle9i Application Developer’s Guide - Advanced Queuing