|
View previous topic :: View next topic
|
| Author |
Message |
Prasoon Baral
New User
Joined: 12 Sep 2008
Posts: 3
Location: India
|
|
|
|
| What problem can occur if all jobs in a system are coded with REGION=4M irrespective of whether the jobs actually required that region or not? It may happen most of the jobs require less storage than 4M. |
|
| Back to top |
|
 |
Bill Dennis
Active Member
Joined: 17 Aug 2007
Posts: 562
Location: Iowa, USA
|
|
|
|
| Coding an overly large REGION has no bad effects. No storage is obtained if it's never asked for. |
|
| Back to top |
|
|
diwa_thilak
Active User
.jpg)
Joined: 13 Jul 2006
Posts: 205
Location: At my desk
|
|
|
|
Hi,
I found the below notes in the internet, thought it might be useful sharing in this forum.
The REGION parameter specifies the maximum size of the execution region for any job step in this job. The value specified is the amount in K (1024 byte units) or M (1024*1024 byte units) which will be the upper limit on the amount of virtual storage that can be obtained via GETMAIN requests by any step in the job.
| Quote: |
"The region size allowed to users can affect performance of the entire system. When there is no limit on region size and the system uses its default values, users might obtain so much space within a region (by repeated requests for small amounts of storage or a single request for a large amount) that no space would remain in the private area for system use. This situation is likely to occur when a program issues a request for storage and specifies a variable length with such a large maximum value that most or all of the space remaining in the private area is allocated to the request. If this program actively uses this large amount of space (to write tables, for example), it can affect central storage (also known as real storage) and thus impact performance."
|
|
|
| Back to top |
|
|
Bill Dennis
Active Member
Joined: 17 Aug 2007
Posts: 562
Location: Iowa, USA
|
|
|
|
| The explanation found by Diwakar shows why it is bad form to routinely code REGION=0M (unlimited), as some folks do. |
|
| Back to top |
|
|
Prasoon Baral
New User
Joined: 12 Sep 2008
Posts: 3
Location: India
|
|
|
|
What I understand is that coding REGION=0M has a detrimental effect on system performance. But if REGION=4M is coded in all jobs then the job does not block the storage until it request for any storage, thus there is no effect on performance.
What will happen if REGION is not coded in the job? Can you suggest the best practice of coding REGION in JCL? |
|
| Back to top |
|
|
dick scherrer
Moderator Emeritus
Joined: 23 Nov 2006
Posts: 19244
Location: Inside the Matrix
|
|
|
|
Hello,
Your best source for that information (it is rather site-specific) would be your system support (or similar) people. They can tell you what class(es) and region specifications are proper for your jobs. |
|
| Back to top |
|
|
Bill Dennis
Active Member
Joined: 17 Aug 2007
Posts: 562
Location: Iowa, USA
|
|
|
|
| Prasoon Baral wrote: |
| What will happen if REGION is not coded in the job? |
If you don't have REGION coded, you will get a default based on the JES2 JOBCLASS definition or other system exit. If not specified, the system default is 1M. |
|
| Back to top |
|
|
Anuj Dhawan
Superior Member
Joined: 22 Apr 2006
Posts: 6250
Location: Mumbai, India
|
|
|
|
Hi,
Just for my .02 cents..
| Prasoon Baral wrote: |
| What I understand is that coding REGION=0M has a detrimental effect on system performance. |
A value of 0K or 0M will allow the program to request the largest available region size, however this specification should be used with caution. From the OS/390 Initialization and Tuning Guide,
"The region size allowed to users can affect performance of the entire system. When there is no limit on region size and the system uses its default values, users might obtain so much space within a region (by repeated requests for small amounts of storage or a single request for a large amount) that no space would remain in the private area for system use. This situation is likely to occur when a program issues a request for storage and specifies a variable length with such a large maximum value that most or all of the space remaining in the private area is allocated to the request. If this program actively uses this large amount of space (to write tables, for example), it can affect central storage (also known as real storage) and thus impact performance." |
|
| Back to top |
|
|
Anuj Dhawan
Superior Member
Joined: 22 Apr 2006
Posts: 6250
Location: Mumbai, India
|
|
|
|
Hi Bill,
| Bill Dennis wrote: |
| If not specified, the system default is 1M. |
Is it a universal concept ? I don't find any reference/s, please assist. |
|
| Back to top |
|
|
Bill Dennis
Active Member
Joined: 17 Aug 2007
Posts: 562
Location: Iowa, USA
|
|
|
|
One place for a default REGION to be set is based on the JES2 JOBCLASS you submit into. Check the JES2 Init and Tuning Reference manual for the defaults for JOBCLASS.
If you can issue commands, try $DJOBCLASS(n) ,where n is your job class, to see your site values. |
|
| Back to top |
|
|
|
|
