Sunday, 11 August 2013

COBOL Feature Affect Run Time Performace

COBOL and Language Environment have several installation and environment tuning features that can enhance the performance of your application. We will now look at some additional factors that should be considered for the application.
Storage Management Tuning
Storage management tuning can reduce the overhead involved in getting and freeing storage for the application program. With proper tuning, several GETMAIN and FREEMAIN calls can be eliminated. To better understand the need for storage tuning, let's look at how storage management works.
First of all, storage management was designed to keep a block of storage only as long as necessary. This means that during the execution of a COBOL program, if any block of storage becomes empty, it will be freed.
This can be beneficial in a transaction environment (or any environment) where you want storage to be freed as soon as possible so that other transactions (or applications) can make efficient use of the storage. However, it can also be detrimental if the last block of storage does not contain enough free space to satisfy a storage request by a library routine. For example, suppose that a library routine needs 2K of storage but there is only 1K of storage available in the last block of storage. The library routine will call storage management to request 2K of storage.
Storage management will determine that there is not enough storage in the last block and issue a GETMAIN to acquire this storage (this GETMAINed size can also be tuned). The library routine will use it and then, when it is done, call storage management to indicate that it no longer needs this 2K of storage.
Storage management, seeing that this block of storage is now empty, will issue a FREEMAIN to release the storage back to the operating system. Now, if this library routine or any other library routine that needs more than 1K of storage is called often, a significant amount of CPU time degradation can result because of the amount of GETMAIN and FREEMAIN activity.
Storage Tuning User Exit
In an environment where Language Environment is being initialized and terminated constantly, such as CICS, IMS, or other transaction processing type of environments, tuning the storage options can improve the overall performance of the application. This helps to reduce the GETMAIN and FREEMAIN activity. The Language Environment storage tuning user exit is one way that you can manage the task of selecting the best values for your environment. The storage tuning user exit allows you to set storage values for your main programs without having to linkedit the values into your load modules.

One way that an assembler program can set up a reusable run-time environment for COBOL is by calling IGZERRE. This module can be invoked to explicitly initialize and terminate COBOL's portion of the LE run-time environment. It allows a non-COBOL, non-LE-conforming program to initialize the LE run-time environment, thereby effectively establishing itself as the main COBOL program. As a result, the use of STOP RUN will cause control to be returned to the caller of the routine that invoked the IGZERRE initialization. IGZERRE is an enhanced version of ILBOSTP0 (for OS/VS COBOL) and accomplishes the same  results as ILBOSTP0. Although, IGZERRE has been designed for Enterprise COBOL, COBOL for OS/390 & VM, COBOL for MVS & VM, COBOL/370, and VS COBOL II applications, it also supports OS/VS COBOL applications. Using IGZERRE has the added benefits of supporting applications running above the 16 MB line, allowing the application to terminate the COBOL portion of the LE run-time environment and improving the performance of the application Using ILBOSTP0 in an LE environment will set up both the OS/VS COBOL and the COBOL portion of the LE environments whereas using IGZERRE will set up only the COBOL portion of the LE environment (the OS/VS COBOL environment will be set up only as needed).

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