JES2

JESJOB ENTRY SUBSYSTEM

Sathya

OS/390 and Job Management• Major goal of an operating system is to process

jobs while making the best use of system resources.

• To obtain that goal, the operating system does resource management, which consists of the following:a) Before job processing, reserve input and output resources for jobs

b) During job processing, manage resources such as processors and storage

c) After job processing, free all resources used by the completed jobs, making the

resources available to other jobs

OS/390 and Job Management

• The MVS system divides the management of jobs and resources with a Job Entry Subsystem (JES).

• JES does job management and resource management before and after job execution,

• MVS does it during job execution. • The JES receives jobs into MVS, schedules them

for processing by MVS, and controls their output processing.

OS/390 and Job Management• The MVS system divides the management of jobs

and resources with a Job Entry Subsystem (JES).• JES does job management and resource

management before and after job execution. • MVS does it during job execution. • The JES

1) Receives jobs into MVS

2) Schedules them for processing by MVS and

3) Controls their output processing.

Types of JES

• JES is of two types:

1) JES2

2) JES3

• JES2 provides the function of Job Entry Subsystem in a Uniplex environment

• JES3 provides the function of Job Entry Subsystem in a Multiiplex environment

Phases of Job Processing

1. Input Phase

2. Conversion Phase

3. Execution (Scheduling) Phase

4. Output Phase

5. Hard Copy Phase

6. Purge Phase

JES2 Job Processing Phases

USER JOB

INPUTPROCESS

CONVERSIONPROCESS

EXECUTIONPROCESS

OUTPUTPROCESS

HARD COPYPROCESS

PURGEPROCESS

INITIATOR

USERPROGRAM

USERREPORTS

Input Phase

• MVS uses Internal Readers to pass to JES2 the JCL for:

1. Started Tasks

2. MOUNT Commands

3. TSO Logon Requests• An Internal Reader is a program that other

programs can use to submit jobs and commands to JES2

• Internal Reader types:

INRDR, STCINRDR, TSOINRDR

Input Phase (contd.)1. JES2 reads job stream (JCL and SYSIN data)

2. JES2 assigns a JOB ID to each job

3. JES2 places the Job’s JCL and SYSIN input data into DASD dataset called SPOOL data sets

(SPOOL stands for Simultaneous Peripheral Operations On-line)

4. JES2 then selects the jobs from spool data sets for processing and subsequent execution

Input Phase (contd.)USER

JOB ‘A’

INPUTPROCESSING

A

A

JCL

SYSIN

SPOOL DATASET

Conversion Phase1. JES2 merges invoked procedure JCL into JOB

A’s job stream

2. The resulting job stream is scanned for syntax errors

3. The JCL statements are prepared for use in initiating the job

4. The JCL for the converted job is stored in a format called Internal Text on the spool data set

Conversion Phase

INPUTPROCESSING

A

A

JCL

SYSIN

CONVERSIONPROCESSING

A INTERNALTEXT

PROCEDURELIBRARY

SPOOL DATASET

Execution Phase

1. JES2 selects JOB A for initiation and execution based on its job class, job selection priority and initiator availability

2. JES2 routines despool the JCL internal text for the initiator to use for our job

3. The JOB A program is initiated

…contd.

Execution Phase (contd.)1. As the JOB A program executes, JES2 routines

despool the SYSIN data and makes it available to the program as is needed

2. JES2 routines spool SYSOUT data as the JOB A program creates it

3. JES2 monitors the number of SYSOUT records and the length of time the program executes. If the limit is exceeded, JES2 will notify the user

Execution PhaseINPUT

PROCESSING

A

A

JCL

SYSIN

CONVERSIONPROCESSING

A INTERNALTEXT

EXECUTIONPROCESSING

A SYSOUT

INITIATOR

USERPROGRAM

SPOOL DATASET

Output and Hard Copy Phase1. When the entire job has concluded, it is

eligible for Output Processing

2. Information about the JOB A’s SYSOUT data sets (such as SYSOUT class, setup requirements, etc) is gathered and summarized in JES2 control blocks

3. The job is ready for Hard Copy processing

4. The SYSOUT data sets are despooled and transferred to printers

Output and Hard Copy PhaseINPUT

PROCESSING

A

A

JCL

SYSIN

A INTERNALTEXT

A SYSOUT

SPOOL DATASET

CONVERSIONPROCESSING

EXECUTIONPROCESSING

OUTPUTPROCESSING

HARD COPYPROCESSING

USERREPORTS

Purge Phase1. After all of JOB A’s data sets have been

printed, the job is ready for Purge Processing

2. Spool spaces is reclaimed for reuse by JES2

3. The Job disappears from the system

4. JES2 no longer knows about the job

Output and Hard Copy PhaseINPUT

PROCESSING

SPOOL DATASET

CONVERSIONPROCESSING

EXECUTIONPROCESSING

OUTPUTPROCESSING

HARD COPYPROCESSING

HARD COPYPROCESSING

Tracking User’s Jobs1. In order to keep track of the user jobs,

JES2 uses internal control blocks2. The control blocks are called JOB QUEUE

ELEMENTS (JQEs)3. JES2 uses the following data sets to keep

track of control blocks:a) SPOOLb) CHECKPOINTc) ALTERNATE or DUPLEX

CHECKPOINT

Job Queue Element Control Blocks(JQE)

1. One JQE is used for each job (batch job, started task or TSO logon)

2. JQE stores:

a) Job’s Name

b) Job Number assigned by JES2

c) Job selection priority

d) SYSOUT routing information

e) Information as to where job’s JCL, SYSIN and SYSOUT data are stored on spool data

set

JOB

INPUT

CONVERSIONQUEUE

PROCESSINGNQUEUE

OUTPUTQUEUE

HARD COPYQUEUE

PURGEQUEUE

CONVERSION PROCESSING OUPUT HARD COPY PURGING

JCLSYSIN

JCL

SYSIN SYSOUT

SYSOUT

NON-PRINTOUTPUT

SPOOLDISK

Checkpoint Data Set1. When JES2 terminates, jobs that have not yet

been executed and SYSOUT data sets that have not been transcribed remain on the Spool data set

2. When JES2 is started again, the jobs and SYSOUT data that remained on the spool can be processed by as if there had been no lapse in the JES2 execution

3. The resumption of JES2 is called WARM start

4. Warm start is possible because of the information stored in Checkpoint data set

JES2 START PROCEDURE