Creation date:10/04/1999
Authored by: Karl Ho
Question:
How to determine an MVS job class?
Answer:
Submitting a job to MVS requires selecting a class card to determine the priority and time requirement for the job. In most cases, class A and B suffice for jobs that execute statistical applications like SPSS and SAS. Both require less than or equal to 2 minutes of CPU time and the latter requires using one tape (e.g. data set is on a tape cartridge). Since these jobs do not need extra resources so they are usually run on top priority, i.e. being executed immediately. For jobs that require more resourses--like more than 2 minutes, more lines than 45,000 or more than one tape--other job class specification is needed. The following lists the specifications for different classes (this information is also available on CMS by typing "help mvs" selecting "jobclass"):
*** JOB CLASS SELECTION ***
CLASS Time/Lines Restrictions No. of Tape
Drives
----------------------------------------------------------
A ........ Time <=2 Lines/1000<=45 .... None
B ........ Same ....................... One
C ........ Same ....................... < Five
D ........ Same ....................... Two
E ........ Same ....................... <=4
A The standard job class (and also the default, if no CLASS=
parameter is specified). Supports no special processing
requirements.
B Allows use of one tape drive (only one tape mounted at a
time).
D Allows use of two tape drives simultaneously. Since these
jobs use all of an available resource (tape drives under MVS),
they are specially scheduled by the academic CPU operator.
Typical turnaround is overnight, but during peak periods of
the semester the turnaround time could be longer.
E For jobs that must run single-threaded but otherwise would be
class A or B. Allows the use of one tape drive. For jobs
that would be class E but require two tape drives, use class D.
C Used by jobs that must, for some reason, run stand-alone; that
is, no other jobs are allowed to run at the same time. Use
of this class requires prior approval by the Academic
Mainframe User Services Manager. Class C necessitates that
a SURF message be sent to the CPU operator indicating what
special processing is required (number of tape drives, data
sets used, etc.). Class C may use all system resources,
including as many tape drives as can be made available under
MVS (normally 2 but up to 4).
The maximum execution time specifiable for "group 1" classes (A
through E) is 2 MINUTES. During the months of April, May, and
June, 1990, over 99% of all jobs executed in less than 2 minutes.
THE MAXIMUM PRINT OUTPUT LIMIT IS 45,000 LINES. A job with a class
specification that conflicts with the limit on estimated time or
lines will be cancelled automatically at read-on time. A job that
exceeds its estimated time or lines while executing will be
cancelled (automatically) at the time of the excess.
Other than the print line limit discussed above, print lines will
no longer be considered in determining job class. (The old
formula, 3 times time plus print lines in thousands less than or
equal to 45, will no longer be used.)
Classes included in the second group (those that exceed the
execution time limit or print line limit) are: J, N, and M. These
jobs will be run as the processing load permits, typically over
night. During peak times of the semester, execution of these jobs
may be delayed by one or more days. These job classes require that
the user submit a SURF message indicating the reason for the job
to be class J, N, or M (i.e. a long run time or large amount of
print output and the number of tape drives used for class N jobs).
Class M jobs require prior approval by the Academic Mainframe User
Services Manager.
CLASS Time/Lines Restrictions NO. of Tape Drives
------------------------------------------------------------
J,N ....... Time >2 OR Lines/1000 >45 .. 0,1,2 Tape Drives
M ......... Same ....................... 3 Tape Drives
Class Description
----- -----------
J Same resources as class A, but with an amount of CPU time
and/or Print lines that exceeds the limit.
N Same resources as class D or B, but with an amount of CPU time
and/or Print lines that exceeds the limit.
M Same as class C, but with an amount of CPU time and/or Print
lines that exceeds the limit.
Class L (for large memory jobs) no longer exists. Any job may
request a region size up to the maximum available; however, any job
requesting large region sizes will be subject to review by the
Academic Mainframe User Services Manager. The user may have to
defend his or her region request. If large region requests become
a problem, class L may be reinstated with little warning.
The old classes I, G, and K are no longer defined; they have had
no practical distinguishing characteristics in a long time.
Last updated: 01/18/06 by Karl Ho