Transcript Slide 1

Introduction to z/OS Basics
Chapter 7: Batch processing and the Job Entry
Subsystem (JES)
Batch processing and JES
© 2006 IBM Corporation
Chapter 07 Batch and JES
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.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Key terms in this chapter
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 batch processing
 procedure
 execution
 purge
 initiator
 queue
 job
 spool
 job entry
subsystem (JES)
 symbolic reference
 output
 workload manager
(WLM)
© 2006 IBM Corporation
Chapter 07 Batch and JES
Job Management
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© 2006 IBM Corporation
Chapter 07 Batch and JES
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:
– Minimal human interaction
– At a scheduled time or on an as-needed basis.
 After a batch job is submitted... normally no further
human interaction until complete.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
What is JES?
 JES manages the input and output job queues and
data.
 JES handles the following aspects of batch work:
– Receives jobs
– Schedules them for execution
– Controls their output processing
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© 2006 IBM Corporation
Chapter 07 Batch and JES
What is JES? (continued)
 z/OS offers two types: JES2 and JES3
 Some differences, but both JES2 and JES3:
– Accept and queue jobs
– Queue jobs for an initiator -- a 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.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Why a JES
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© 2006 IBM Corporation
Chapter 07 Batch and JES
JES FUNCTIONS
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© 2006 IBM Corporation
Chapter 07 Batch and JES
JCL Related Actions
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Phases of Job Processing
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Batch flow (simplified)
JCLProcessing
JES
JOBs
Initiator
ca
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In-itia
- Execution
submit
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- Cleanup
- Execution
- Cleanup
Printer
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© 2006 IBM Corporation
Chapter 07 Batch and JES
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.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
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

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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.
© 2006 IBM Corporation
Chapter 07 Batch and JES
Symbolic references to files ...DD Names
 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.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
How a symbolic file system is used
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© 2006 IBM Corporation
Chapter 07 Batch and JES
How a symbolic file system is used (continued)
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© 2006 IBM Corporation
Chapter 07 Batch and JES
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.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Related actions with JCL
ITUSERACTIO
NS
Determ
ine
theneed
and
characteristics
of theJob
Create
theJCL
SYSTEMACTIO
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JESinterprets
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passesit to
z/OSinitiator
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theJob
z/OS
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anages
eachstep
of execution
System
M
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User
views
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interprets
output
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JESprints
output
JEScollects
theoutput and
inform
ation
about theJob
© 2006 IBM Corporation
Chapter 07 Batch and JES
Spooling
JCL
program
JES 1
read 2
//DD1 DD*
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//DD2 DDSYSOUT=A
JES 4
SYSOUT
write 3
Printer
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Two-step job
First step
Master
Second step
Program
Tape
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Master
Updates
Program
Master
Printer
© 2006 IBM Corporation
Chapter 07 Batch and JES
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
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Phases of job flow: input
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Phases of job flow: conversion
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Phases of job flow: execution
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Phases of job flow: output and hardcopy
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Phases of job flow: purge
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Job flow through the system
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© 2006 IBM Corporation
Chapter 07 Batch and JES
Benefits of JES systems and Sysout printing
 Fewer Printers needed – Sysout provides virtual
printers
 Printers run faster – JES create channel programs
that “batch” print operations
 Printers more efficient – Don't wait for application to
generate next message
 Jobs execute faster – Virtual printers run at memory
speed (block msgs into spool buffers)
 CPUs more efficient – Fewer IO interrupts because of
“batch” print operations
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© 2006 IBM Corporation
Chapter 07 Batch and JES
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 by
providing its own device allocation.
 Most installations use JES2, as do the examples in this text.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
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.
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© 2006 IBM Corporation
Chapter 07 Batch and JES
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.
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© 2006 IBM Corporation