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Introduction to the new mainframe
Chapter 7: Batch processing and the Job EntrySubsystem (JES)
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Introduction to the new mainframe
Chapter 7 objectives
Be able to:
Give an overview of batch processing and
system.
Explain how the job entry subsystem
governs t e ow o wor t roug az/OS system.
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Introduction to the new mainframe
Key terms in this chapter
a c process ng
execution
initiator
proce ure
purge
queue
job
job entry subsystem (JES)
spool
symbolic reference
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Introduction to the new mainframe
What is batch processing?
Much of the work running on z/OS consists of programs
called batch jobs.
Batch processingis used for programs that can be
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 thejob until it is complete.
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Introduction to the new mainframe
What is JES?
In the z/OS operating system, JESmanages the input and
output job queues and data.an es e o ow ng aspec s o a c process ng or
z/OS:
Schedules them for processing by z/OS
Controls their output processing
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Introduction to the new mainframe
What is JES? (continued)
z/OS offers two types: JES2 and JES3
Some important differences, but both JES2 and JES3: ccept and queue jobs submitted for execution
Queue jobs for an initiator-- a JES program that requests the nextob in the ueue
Accept outputfrom a job while it is running and queue the output
Can print the output, or save it on spoolfor an output manager toretr eve.
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Introduction to the new mainframe
What is JES? (continued)
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Introduction to the new mainframe
Batch flow (simplified)
rocess ng
InitiatorJES
-
- Execution- Cleanup
SPOOLSPOOL
n a or
-Allocation- Execution
submit
-
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Printer
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Introduction to the new mainframe
What is spooling?
Spoolingis a method for queuing and holding data for input
or output.uses one or more s a a se s or spoo ng.
Input jobs and printed output from many jobs are stored in.
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Introduction to the new mainframe
What an initiator does
To run multiple jobs asynchronously, z/OS uses
initiators to:
Ensure that single-user devices (tape drives) are allocatedcorrectly
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
is one of the defining characteristics of the operatings stem.
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Introduction to the new mainframe
Symbolic references to files
rather than actual file names.
The use of symbolic references provides a namingredirection between a data set-related name used in aprogram and the actual data set used during execution
of that program.
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Introduction to the new mainframe
How a symbolic file system is used
DDNAME DSNAME
=
program JCL for JOB
READ FILE=XYZ
...
//XYZ DD DSNAME=MY.PAYROLL MY.PAYROLL
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Introduction to the new mainframe
How a symbolic file system is used (continued)DDNAME DSNAME
OPEN FILE=XYZ
READ FILE=XYZ
program JCL for JOB
...
CLOSE FILE=XYZ
//XYZ DD DSNAME=DIV1.PAYROLLDIV1.PAYROLL
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Introduction to the new mainframe
JES, job management, and JCL
Job control language (JCL) is the language used by a
batch job to request resources and services from the.
Through JCL, you specify:
.
Which resources (programs, files, memory) and services areneeded from the system to process your program.
The use of JCL is covered in detail in the next module.
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Related actions with JCLIT USER ACTIONS SYSTEM ACTIONS
Determinethe need
and
characteristicsof the Job
Create
the JCL
Submit
the Job
JES interpretsJCL and
passes it toz/OS initiator
z/OS
manageseach step
of execution
SystemMessages
JES collectsUser
JES printsoutput
the output andinformation
about the Job
andinterprets
output
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Introduction to the new mainframe
SpoolingJCL
program
22read
//DD1 DD *
...............
data
//DD1 DD *
...............
data
//DD1 DD *
...............
data
11JES
spool
/*
//DD2 DD SYSOUT=A
...............
/*
//DD2 DD SYSOUT=A
...............
/*
//DD2 DD SYSOUT=A
...............
SYSOUT 44
JES
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Two-step job
First step
Updates MasterMaster
Second step
Program Program
Tape PrinterMaster
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Introduction to the new mainframe
Job flow through the system
During execution, a job goes through the following
phases:
Conversion
Processin
Output Print (to hardcopy or a console display)
Purge
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Phases of job flow: input
JOB
CONVERSIONQUEUE
INPUT CONVERSION PROCESSING HARD-COPY PURGEOUTPUT
JCL & SYSIN
SPOOLSPOOL
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Phases of job flow: conversion
EXECUTIONQUEUE
CONVERSIONQUEUE
INPUT CONVERSION PROCESSING HARD-COPY PURGEOUTPUT
JCL
SPOOLSPOOLDISKDISK
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Phases of job flow: executionJOB
OUTPUTQUEUE
EXECUTIONQUEUE
INPUT CONVERSION PROCESSING HARD-COPY PURGEOUTPUT
SYSOUTSYSIN
SPOOLSPOOLDISK
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Phases of job flow: output and hardcopy
JOB
PURGEQUEUE
HARD-COPYQUEUE
OUTPUTQUEUE
INPUT CONVERSION PROCESSING HARD-COPY PURGEOUTPUT
SYSOUT
NON-PRINT/PUNCHOUTPUT
SPOOLSPOOL
DISKDISK
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Phases of job flow: purge
JOB
PURGEQUEUE
INPUT CONVERSION PROCESSING HARD-COPY PURGEOUTPUT
SPOOLSPOOL
DISKDISK
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Job flow through the system
JOB
PURGEQUEUEHARD-COPYQUEUEOUTPUTQUEUEEXECUTIONQUEUECONVERSIONQUEUE
INPUT CONVERSION PROCESSING HARD-COPY PURGEOUTPUT
SYSOUTSYSIN
SYSOUT
JCL
JCL & SYSIN
(NJE)
SPOOLSPOOL
DISKDISK
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Introduction to the new mainframe
JES2 compared to JES3
n a mu t -processor con gurat on:
JES2:
job output processing.
It is possible to configure JES2 to share spool and checkpoint data sets- .
JES3: Centralized control over processing through a single global JES3
processor, w c oes o se ec on, sc e u ng, an ev ce a oca onthe other JES3 systems.
The centralized control of JES3 provides increased job schedulingcontrol, deadline scheduling capabilities, and increased control byproviding its own device allocation.
Most installations use JES2, as do the examples in this text.
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What is workload manager?
Workload manager (WLM):
The component of z/OS that manages the processing of
goals, such as response time.
Also manages the use of system resources, such as processorsan storage, to accomp s t ese goa s.
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Summary
atc process ng s a un amenta unct on o z .
z/OS shares with JES the management of jobs and resources.
,processing, and controls their output.
JES manages jobs in queues.
An initiator sets up the necessary environment for running abatch job. Multiple initiators permit the parallel execution ofbatch obs.
During the life of a job, both JES and the z/OS base controlprogram control different phases of the overall processing.
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