1. Introduction to z/OS Basics © 2006 IBM Corporation Chapter 7: Batch processing and the Job Entry Subsystem (JES) Batch processing and JES

2. Chapter 07 Batch and JES © 2006 IBM Corporation 2 Chapter objectives  Be able to:  Give an overview of batch processing and how work is initiated and managed in the system.  Explain how the job entry subsystem (JES) governs the flow of work through a z/OS system.

3. Chapter 07 Batch and JES © 2006 IBM Corporation 3 Key terms in this chapter  batch processing  execution  initiator  job  job entry subsystem (JES)  output  procedure  purge  queue  spool  symbolic reference  workload manager (WLM)

4. Chapter 07 Batch and JES © 2006 IBM Corporation 4 Job Management

5. Chapter 07 Batch and JES © 2006 IBM Corporation 5 What is batch processing?  Much of the work running on z/OS consists of programs called batch jobs.  Batch processing is used for programs that can be executed: –With minimal human interaction –At a scheduled time or on an as-needed basis.  After a batch job is submitted to the system for execution, there is normally no further human interaction with the job until it is complete.  Use Job Control Language (JCL) to tell the computer what to do –Who your are –What program to run –Where input and output are located –When a job is to run

6. Chapter 07 Batch and JES © 2006 IBM Corporation 6 What is JES?  Job Entry Subsystem  In the z/OS operating system, JES manages the input and output job queues and data.  JES handles the following aspects of batch processing for z/OS: –Receives jobs into the operating system –Schedules them for processing by z/OS –Controls their output processing

7. Chapter 07 Batch and JES © 2006 IBM Corporation 7 What is JES? (continued)  z/OS offers two types: JES2 and JES3  Some important differences, but both JES2 and JES3: –Accept and queue jobs submitted for execution From ISPF through the SUBMIT command Over the network From a running program From a card reader – very rare –Queue jobs waiting to be executed –Queue jobs for an initiator -- a JES program that requests the next job in the queue –Accept output from a job while it is running and queue the output –Can print the output, or save it on spool for an output manager to retrieve.

8. Chapter 07 Batch and JES © 2006 IBM Corporation 8 Why do we need JES

9. Chapter 07 Batch and JES © 2006 IBM Corporation 9 JES FUNCTIONS

10. Chapter 07 Batch and JES © 2006 IBM Corporation 10 JCL Related Actions

11. Chapter 07 Batch and JES © 2006 IBM Corporation 11 Phases of Job Processing

12. Chapter 07 Batch and JES © 2006 IBM Corporation 12 Batch flow (simplified)

13. Chapter 07 Batch and JES © 2006 IBM Corporation 13 What is spooling?  Spooling is a method for queuing and holding data for input or output.  JES uses one or more disk data sets for spooling.  Input jobs and printed output from many jobs are stored in the single (conceptual) spool data set.

14. Chapter 07 Batch and JES © 2006 IBM Corporation 14 What an initiator does  To run multiple jobs asynchronously, z/OS uses initiators to: –Ensure that jobs do not conflict in data set usage –Ensure that single-user devices (tape drives) are allocated correctly –Find executable programs requested by jobs –Clean up after the job ends and request the next job  Preventing two users from accessing the same data at the same time is critical to z/OS and the ability to do this is one of the defining characteristics of the operating system.

15. Chapter 07 Batch and JES © 2006 IBM Corporation 15 Symbolic references to files  z/OS normally uses symbolic references to files (data sets) rather than actual file names.  The use of symbolic references provides a naming redirection between a data set-related name used in a program and the actual data set used during execution of that program.

16. Chapter 07 Batch and JES © 2006 IBM Corporation 16 How a symbolic file system is used

17. Chapter 07 Batch and JES © 2006 IBM Corporation 17 How a symbolic file system is used (continued)

18. Chapter 07 Batch and JES © 2006 IBM Corporation 18 JES, job management, and JCL  Job control language (JCL) is the language used by a batch job to request resources and services from the operating system.  Through JCL, you specify: –Who you are (important for security reasons). –Which resources (programs, files, memory) and services are needed from the system to process your program.  The use of JCL is covered in detail in the next module.  Example Batch job follows

19. Chapter 07 Batch and JES © 2006 IBM Corporation Procedure to Compile, link-edit, and execute programs 000010 //IGYWCLG PROC LNGPRFX='IGY.V3R2M0',SYSLBLK=3200, 000020 // LIBPRFX='CEE',GOPGM=GO 000030 //* 000040 //********************************************************************* 000050 //* * 000060 //* Enterprise COBOL for z/OS and OS/390 * 000070 //* Version 3 Release 2 Modification 0 * 000080 //* * 000090 //* LICENSED MATERIALS - PROPERTY OF IBM. * 000100 //* * 000110 //* 5655-G53 5648-A25 (C) COPYRIGHT IBM CORP. 1991, 2002 * 000120 //* ALL RIGHTS RESERVED * 000130 //* * 000140 //* US GOVERNMENT USERS RESTRICTED RIGHTS - USE, * 000150 //* DUPLICATION OR DISCLOSURE RESTRICTED BY GSA * 000160 //* ADP SCHEDULE CONTRACT WITH IBM CORP. * 000170 //* * 000180 //********************************************************************* 19

20. Chapter 07 Batch and JES © 2006 IBM Corporation Procedure to Compile, link-edit, and execute programs 000190 //* 000300 //COBOL EXEC PGM=IGYCRCTL,REGION=2048K 000310 //STEPLIB DD DSNAME=&LNGPRFX..SIGYCOMP, 000320 // DISP=SHR 000330 //SYSPRINT DD SYSOUT=* 000340 //SYSLIN DD DSNAME=&&LOADSET,UNIT=SYSDA, 000350 // DISP=(MOD,PASS),SPACE=(TRK,(3,3)), 000360 // DCB=(BLKSIZE=&SYSLBLK) 000370 //SYSUT1 DD UNIT=SYSDA,SPACE=(CYL,(1,1)) 000440 //LKED EXEC PGM=HEWL,COND=(8,LT,COBOL),REGION=1024K 000450 //SYSLIB DD DSNAME=&LIBPRFX..SCEELKED, 000460 // DISP=SHR 000470 //SYSPRINT DD SYSOUT=* 000480 //SYSLIN DD DSNAME=&&LOADSET,DISP=(OLD,DELETE) 000490 // DD DDNAME=SYSIN 000500 //SYSLMOD DD DSNAME=&&GOSET(&GOPGM),SPACE=(TRK,(10,10,1)), 000510 // UNIT=SYSDA,DISP=(MOD,PASS) 000520 //SYSUT1 DD UNIT=SYSDA,SPACE=(TRK,(10,10)) 000530 //GO EXEC PGM=*.LKED.SYSLMOD,COND=((8,LT,COBOL),(4,LT,LKED)), 20 Identifies COBOL compiler Describes output of compiler Second Step: perform link-edit

21. Chapter 07 Batch and JES © 2006 IBM Corporation Procedure to Compile, link-edit, and execute programs 000540 // REGION=2048K 000550 //STEPLIB DD DSNAME=&LIBPRFX..SCEERUN, 000560 // DISP=SHR 000570 //SYSPRINT DD SYSOUT=* 000580 //CEEDUMP DD SYSOUT=* 000590 //SYSUDUMP DD SYSOUT=* 21

22. Chapter 07 Batch and JES © 2006 IBM Corporation 22 Related actions with JCL

23. Chapter 07 Batch and JES © 2006 IBM Corporation 23 Spooling Spooling is the means by which the system manipulates its work. Using storage on direct access storage devices as buffer storage to reduce processing delays Reading and writing input and output streams on an intermediate device Performing an operation such as printing while the computer is busy. Used to improve performance of computer

24. Chapter 07 Batch and JES © 2006 IBM Corporation 24 Two-step job Make a backup copy of one master file and then update the master file with records read in from another file (update file). 1.Read master file and write it to tape 2.Read record from update file and search for it in the master file. 1.Update record if found, otherwise adds new record

25. Chapter 07 Batch and JES © 2006 IBM Corporation Build a Job with Two Steps that Specify:  Who you are  What resources are needed by the job, such as the following: –Load the backup program (that you already have compiled). –How much memory the system needs to allocate to accommodate the backup program, I/O buffers, and working areas. –Make accessible to the backup program an output tape data set to receive the backup, a copy, and the master file data set itself. –At program end indicate to the operating system that now your update program needs to be loaded into memory (however, this should not be done if the backup program failed). –Make accessible to the update program the update file and master file. –Make accessible to your program a printer for eventual messages. 25

26. Chapter 07 Batch and JES © 2006 IBM Corporation 26 Job flow through the system  During execution, a job goes through the following phases: – Input – Conversion – Processing – Output – Print (to hardcopy or a console display) – Purge

27. Chapter 07 Batch and JES © 2006 IBM Corporation 27 Phases of job flow: input Input: Accepts job in form of input stream Conversion: analyze and merge JCL with library procedures

28. Chapter 07 Batch and JES © 2006 IBM Corporation 28 Phases of job flow: conversion JES2 converts the composite JCL into converter/interpreter text that both JES2 and the initiator can recognize. Next, JES2 stores the converter/interpreter text on the spool data set.

29. Chapter 07 Batch and JES © 2006 IBM Corporation 29 Phases of job flow: execution In the processing phase, JES2 responds to requests for jobs from the initiators. JES2 selects jobs that are waiting to run from a job queue and sends them to initiators

30. Chapter 07 Batch and JES © 2006 IBM Corporation 30 Phases of job flow: output and hardcopy Output: JES2 controls all SYSOUT processing. SYSOUT is system-produced output; that is, all output produced by, or for, a job. Hardcopy: JES2 selects output for processing from the output queues by output class, route code, priority, and other criteria.

31. Chapter 07 Batch and JES © 2006 IBM Corporation 31 Phases of job flow: purge Purge: When all processing for a job completes, JES2 releases the spool space assigned to the job, making the space available for allocation to subsequent jobs.

32. Chapter 07 Batch and JES © 2006 IBM Corporation 32 Job flow through the system

33. Chapter 07 Batch and JES © 2006 IBM Corporation 33 JES2 compared to JES3  In a multi-processor configuration:  JES2: –Each JES2 processor controls its own job input, job scheduling, and job output processing. –It is possible to configure JES2 to share spool and checkpoint data sets with other JES2 systems (multi-access spool or MAS).  JES3: –Centralized control over processing through a single global JES3 processor, which does job selection, scheduling, and device allocation the other JES3 systems. –The centralized control of JES3 provides increased job scheduling control, deadline scheduling capabilities, and increased control by providing its own device allocation.  Most installations use JES2, as do the examples in this text.

34. Chapter 07 Batch and JES © 2006 IBM Corporation 34 What is workload manager?  Workload manager (WLM):  The component of z/OS that manages the processing of workload in the system according to the company’s business goals, such as response time.  Also manages the use of system resources, such as processors and storage, to accomplish these goals.

35. Chapter 07 Batch and JES © 2006 IBM Corporation 35 Summary  Batch processing is a fundamental function of z/OS.  z/OS shares with JES the management of jobs and resources.  JES receives jobs into the system, schedules them for processing, and controls their output.  JES manages jobs in queues.  An initiator sets up the necessary environment for running a batch job. Multiple initiators permit the parallel execution of batch jobs.  During the life of a job, both JES and the z/OS base control program control different phases of the overall processing.