Oracle7 Server Administrator's Guide
SNP Background Processes
This section describes SNP background processes and their role in managing job queues, and includes the following topics:
You can schedule routines to be performed periodically using the job queue. A routine is any PL/SQL code. To schedule a job, you submit it to the job queue and specify the frequency at which the job is to be run. You can also alter, disable, or delete jobs you have submitted.
To maximize performance and accommodate many users, a multi-process Oracle7 system uses some additional processes called background processes. Background processes consolidate functions that would otherwise be handled by multiple Oracle programs running for each user process. Background processes asynchronously perform I/O and monitor other Oracle processes to provide increased parallelism for better performance and reliability.
SNP background processes execute job queues. SNP processes periodically wake up and execute any queued jobs that are due to be run. You must have at least one SNP process running to execute your queued jobs in the background.
SNP background processes differ from other Oracle7 background processes, in that the failure of an SNP process does not cause the instance to fail. If an SNP process fails, Oracle7 restarts it.
See Also: For more information on background processes, see Oracle7 Server Concepts.
Multiple SNP Processes
An instance can have up to ten SNP processes, named SNP0 to SNP9. If an instance has multiple SNP processes, the task of executing queued jobs can be shared across these processes, thus improving performance. Note, however, that each job is run at any point in time by only one process. A single job cannot be shared simultaneously by multiple SNP processes.
Starting Up SNP Processes
Job queue initialization parameters enable you to control the operation of the SNP background processes. When you set these parameters in the initialization parameter file for an instance, they take effect the next time you start the instance.
Table 7 - 1 describes the job queue initialization parameters.
| Parameter Name
| Description
|
|
| JOB_QUEUE_PROCESSES
| Default:
| 0
|
|
| Range of values:
| 0...10
|
|
| Multiple instances:
| can have different values
|
|
| Sets the number of SNP background processes per instance.
|
|
| JOB_QUEUE_INTERVAL
| Default:
| 60 (seconds)
|
|
| Range of values:
| 1...3600 (seconds)
|
|
| Multiple instances:
| can have different values
|
|
| Sets the interval between wake-ups for the SNP background processes of the instance.
|
|
Table 7 - 1. Job Queue Initialization Parameters