Sunday, 11 August 2013

COBOL Run-Time Performance Part 1

Selecting the proper run-time options is another factor that affects the performance of a COBOL application.
Therefore, it is important for the system programmer responsible for installing and setting up the LE environment to work with the application programmers so that the proper run-time options are set up correctly for your installation.
Let's look at some of the options that can help to improve the performance of the individual application, as well as the overall LE run-time environment.
AIXBLD : The AIXBLD option allows alternate indexes to be built at run time. However, this may adversely affect the run-time performance of the application. It is much more efficient to use Access Method Services to build the alternate indexes before running the COBOL application than using the NOAIXBLD run-time option. Note that AIXBLD is not supported when VSAM datasets are accessed in RLS mode.
ALL31 : The ALL31 option allows LE to take advantage of knowing that there are no AMODE(24) routines in the application. ALL31(ON) specifies that the entire application will run in AMODE(31). This can help to improve the performance for an all AMODE(31) application because LE can minimize the amount of mode switching across calls to common run-time library routines. Additionally, using ALL31(ON) will help to relieve some below the line virtual storage constraint problems, since less below the line storage is used.
CHECK : The CHECK option activates the additional code generated by the SSRANGE compiler option, which requires more CPU time resources for the verification of the subscripts, indexes, and reference modification expressions. Using the CHECK(OFF) run-time option deactivates this code but still requires some additional CPU time resources at every use of a subscript, index, or reference modification expression to determine that this check is not desired during the particular run of the program. This option has an effect only on a program that has been compiled with the SSRANGE compiler option.
DEBUG : The DEBUG option activates the COBOL batch debugging features specified by the USE FOR DEBUGGING declarative. This may add some additional overhead to process the debugging statements. This option has an effect only on a program that has the USE FOR DEBUGGING declarative.
RPTOPTS : The RPTOPTS option allows you to get a report of the run-time options that were in use during the execution of an application. This report is produced after the application has terminated. Thus, if the application abends, the report may not be generated. Generating the report can result in some additional overhead. Specifying RPTOPTS(OFF) will eliminate this overhead.
RPTSTG : The RPTSTG option allows you to get a report on the storage that was used by an application. This report is produced after the application has terminated. Thus, if the application abends, the report may not be generated. The data from this report can help you fine tune the storage parameters for the application, reducing the number of times that the LE storage manager must make system requests to acquire or free storage. Collecting the data and generating the report can result in some additional overhead. Specifying RPTSTG(OFF) will eliminate this overhead.
RTERUS : The RTEREUS option causes the LE run-time environment to be initialized for reusability when the first COBOL program is invoked. The LE run-time environment remains initialized (all COBOL programs and their work areas are kept in storage) in addition to keeping the library routines initialized and in storage. This means that, for subsequent invocations of COBOL programs, most of the run-time environment initialization will be bypassed. Most of the run-time termination will also be bypassed, unless a STOP RUN is executed or unless an explicit call to terminate the environment is made (Note: using STOP RUN results in control being returned to the caller of the routine that invoked the first COBOL program, terminating the reusable run-time environment).
Because of the effect that the STOP RUN statement has on the run-time environment, you should change all STOP RUN statements to GOBACK statements in order to get the benefit of RTEREUS. The most noticeable impact will be on the performance of a non-COBOL driver repeatedly calling a COBOL subprogram (for example, an assembler driver that repeatedly calls COBOL applications). The RTEREUS option helps in this case. However, using the RTEREUS option does affect the semantics of the COBOL application: each COBOL program will now be considered to be a subprogram and will be entered in its last-used state on subsequent invocations (if you want the program to be entered in its initial state, you can use the INITIAL clause on the PROGRAM-ID statement).
STORAGE : The first parameter of this option initializes all heap allocations, including all external data records acquired by a program, to the specified value when the storage for the external data is allocated. This also includes the WORKING-STORAGE acquired by a RENT program (unless a VALUE clause is used on the data item) when the program is first called or, for dynamic calls, when the program is canceled and then called again. Storage is not initialized on subsequent calls to the program. This can result in some overhead at run time depending on the number of external data records in the program and the size of the WORKING-STORAGE section.

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