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.

A REGION= value on the JOB statement will override any REGION= specified on an EXEC statement in the job.

The current installation default is 4M. A specification of 10M is the largest specification allowed without consultation with Technical Services.

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."

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