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What is Subsystem?

What is Subsystem?


Subsystem is an operating environment, defined by subsystem description, where the system coordinates processing and resources.

These can be used to control how different jobs run on your system and how much resources are allocated to different jobs.

Here are simple examples on how subsystem can be used.

E.g.1:

For instance – in a mostly interactive environment you may want all your batch jobs to run in a batch subsystem which has 25% of your systems memory allocated to it, while your interactive jobs run in a subsystem which has 75% of your systems memory allocated to it. In a mostly batch processing environment you may want more memory allocated to your batch jobs and less for your interactive.

E.g.2:

If you have several customers that use your AS/400 with different agreements on how many users can access the system – you can allocate subsystems based on device IDs and you can use different subsystems to limit the number of active jobs per subsystem. So if all customer A’s workstation devices start with an A, all their interactive jobs would go to subsystem A, etc.

Each Subsystem has its own run time attribute that is used by the job to have it executed under that environment.

Subsystems would generally classify based on the Type of Jobs that are being run. Subsystem can also handle different types of Jobs.

Below are the few simple IBM Supplied Subsystems.

1. QBASE - Supports Interactive, Batch and Communication Jobs.

2. QSPL - Spool Subsystem that supports reader/writer Jobs.

3. QCTL - Controlling Subsystem that starts up the system console.

4. QINTER - Supports Interactive Jobs.

5. QBATCH - Supports Batch Jobs.

6. QCMN - Supports all communication Jobs.

How to Create Subsystem?

We can create our own subsystems to run interactive/batch jobs.

We can start or end subsystems whenever we need, without disturbing our other system jobs (Jobs running under QBATCH/QINTER/Our own Subsystem).

Basic elements needed to create subsystem.

a. Subsystem Description

b. Job Queue

c. Class Object

d. Routing Entries

Steps to Create Subsystem:

Create Subsystem Description (CRTSBSD):

CRTSBSD SBSD(LIBRARY/TESTSBSD)          
        POOLS((1 *BASE))                
        MAXJOBS(50)                     
        TEXT('My subsystem description')

Subsystem ‘TESTSBSD’ will run in Pool ‘1’ and will use *BASE for main memory storage.

There can be maximum of 50 Jobs inside the subsystem at a time.

Create Job Queue (CRTJOBQ):

CRTJOBQ JOBQ(LIBRARY/TESTJOBQ) TEXT('My job queue')

Add Job Queue Entry (ADDJOBQE):

Once the JOBQ is created, We need to attach the JOBQ to subsystem.

ADDJOBQE SBSD(LIBRARY/TESTSBSD) JOBQ(LIBRARY/TESTJOBQ) MAXACT(20)

MAXACT denotes the number jobs that can be processed at a time under this JOBQ.

Create Class (CRTCLS):

Class defines the run time attributes like, Run priority, Time Slice, Default wait time, Maximum temporary storage etc.

CRTCLS    CLS(LIBRARY/TESTCLS) RUNPTY(50)

Add Routing Entry (ADDRTGE):

ADDRTGE SBSD(LIBRARY/TESTSBSD) SEQNBR(9999) CMPVAL(*ANY) PGM(SYS/QCMD) CLS(LIBRARY/TESTCLS)

Start Subsystem (STRSBS):

STRSBS SBSD(LIBRARY/TESTSBSD)

Once the Subsystem is started, it can be used to submit the jobs.

End Subsystem (ENDSBS):

Subsystem can be end by using ENDSBS command.

ENDSBS SBSD(TESTSBSD)

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