10.3.3.2 Serializing Job Execution

JES2 does not guarantee that jobs will run in the order they are submitted. If you need to make certain jobs run in order or you need dependent job control, you should submit them one at a time or use an automated job scheduling product such as OPC/A.

10.3.3.3 Time Event Scheduling

POWER supports the scheduling of job submission based on a one-time or repetitive schedule such as daily, weekly on a given day and time, and so on.

JES2 has a primitive automatic command scheduling facility, but you will probably need an automated scheduling package in OS/390 to do the same thing.

10.3.3.4 Additional Job Scheduling Functions with MVS/JES2

The following functions are not available in VSE/POWER, but may be exploited in OS/390 JES2:

Priority Aging When ¢Priority aging¢ is on, JES2 will periodically increase a jobs priority for execution or printing, based on the length of time the job has been in the queue. For example, JES2 can be instructed to raise a job¢s priority by 1 every hour that it¢s been on the queue.

Time Limits A job¢s priority can be based upon its estimated elapsed time which can be specified on JECL statement or through JES2 exits. See the JOBPRTY JES2 initialization statement. (The installation can choose to cancel jobs exceeding their estimated time through initialization parameters or exits.)

The CPU time of a job can also be specified on the JOB or EXEC JCL statement, and controlled by SMF exits.

Output Limits The output priority can be based upon its actual output size according to the OUTPRTY JES2 initialization statement.

Job limits are based on JES2 estimated counts, JECL statements and JES2 exits, and can be extended or controlled by JES2 Exit 9.

Data set limits are based on the OUTLIM parameter of the DD statement. They can be extended or controlled by the IEFUSO SMF exit.

JCL Conversion This happens much earlier in the job¢s processing in OS/390 than in VSE. JECL (JES2 control cards) are processed at reader time. JCL is converted soon after reader time, then interpreted during step initialization.

Resource Affinity With OS/390 Version 2 Release 4, jobs can be selected according to the scheduling environment specified on the JOB card, and based on the availability or abstract resources as controlled by the workload manager.

Workload Managed Batch Initiators With OS/390 Rel.4, jobs can be selected based on installation defined performance objectives when running in ²Goal² mode.

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IBM OS/390 manual Serializing Job Execution, Time Event Scheduling, Additional Job Scheduling Functions with MVS/JES2

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.