HLI: Model 204 parameters

Overview

This topic provides summary information about Model 204 parameters for application programmers who are using the Host Language Interface facility.

See the list of Model 204 parameters for more information about the use and specifications of all Model 204 parameters.

Refer to the Rocket Model 204 Host Language Interface Reference Manual for more information about IFAM1, IFAM2, and IFAM4 jobs.

Model 204 parameters

Parameters are variables that control or describe the Model 204 system.

The HLI application program passes to Model 204 the information pertinent to each HLI call, such as what file to open or what records to count, in a parameter list with the call. Model 204 passes information back to the application program, such as the count, as output parameters.

Refer to the Rocket Model 204 Host Language Interface Reference Manual for a description of HLI calls and their particular parameter lists.

All parameters have default values. You can set parameters to different values to tailor system performance to a particular installation's or user's requirements.

On an IFSTRT thread, you can retrieve the current value of any parameter using the IFEPRM call. You can modify the value of certain parameters using the IFRPRM and IFUTBL calls.

On an IFDIAL thread, you can use these Model 204 commands: VIEW, RESET, and UTABLE.

The basic types of Model 204 parameters are listed in the following table.

Types of Model 204 parameters
Parameter type	Function
System	Controls the operation of Model 204 as a whole.
User environment control	Controls the operation of a particular user's terminal or the characteristics of the system responses toward that user.
File	Affects the organization or structures of Model 204 files.

The following sections describe these types of parameters.

System parameters

System parameters control the operation of the Model 204 system as a whole.

System parameter values affect such characteristics as the frequency of checkpoints, the maximum number of files and groups that can be opened concurrently, the size of the buffer pool, the size and number of user work areas, and the maximum length of HLI call parameters.

For example, the following parameters control the maximum length of HLI call parameters and are critical for proper HLI processing:

Parameter	Meaning	Function	Default
`LIBUFF`	Input buffer length	Specifies the maximum length allowed for string values passed to Model 204 in HLI call parameters.	255 bytes
`LOBUFF`	Logical line output buffer length	Specifies the length of the logical line output buffer for output parameters returned by Model 204 to the HLI program.	256 bytes

Other system parameters, such as LAUDIT, SYSOPT, and IFAMBS, are also important for HLI processing.

Setting system parameters for an HLI job

System parameters that can be set for an HLI job are set on the EXEC statement of the Model 204 region or on a parameter line read at system initialization.

In an IFAM1 job, you can specify system parameters in the IFSTRT call or in the IFSETUP call for an IFDIAL thread. In an IFAM4 job, you can specify system parameters in the EXEC statement in the job setup.

Note: After the Model 204 region has been initialized, most system parameters cannot be reset.

For more information, see Using HLI and batch configurations.

User environment control parameters

User environment control parameters (that is, User 0 parameters) affect the operation of a particular user's terminal or the characteristics of system responses toward that user. For example, the access method and device type are required parameter specifications for a user. Each user must be defined to Model 204.

In an IFAM1 job, specify the user parameters in the IFSTRT call. In an IFAM4 job, specify the user parameters in the CCAIN input file in the job setup. Refer to the Rocket Model 204 Host Language Interface Reference Manual for a description of IFAM1 and IFAM4 jobs.

For more information, see User environment control parameters.

Buffer size and IODEV parameters for an IFDIAL thread

The maximum length of a data area that can be transferred over an IFDIAL thread is 32763 bytes. The maximum length affects application developers who use the IFDIAL thread as well as Model 204 system administrators who must set up the size parameters.

The system administrator of a Model 204 installation can tune the size parameters so that the best performance versus memory ratio can be achieved. Model 204 determines the size of buffers in the User 0 MAX(OUTMRL,INMRL) parameter.

Refer to the Rocket Model 204 Host Language Interface Reference Manual for detailed information about transferring data on an IFDIAL thread and related size considerations.

There are performance considerations in implementing the communication buffer for an IFDIAL thread by setting User 0 parameters for IODEV=29 (in z/OS and z/VSE) or IODEV=39 (in z/VM). For more information, see User environment control parameters.

User table parameters

User table parameters affect the size of the tables in a user's work area.

Model 204 holds an area of memory known as server area, which contains the information needed to describe the operation of an individual user. The server is divided into tables, each of which contains a specific type of data.

The user table parameters determine the size of these tables. The size of user tables can be reset with the IFUTBL call.

See HLI: Model 204 tables for more information about user work areas and table parameters.

File parameters

File parameters affect the organization, structure, and allocation of Model 204 files.

Some file parameters are set when a file is created. The Model 204 file manager determines these parameters, which usually cannot be changed after the file is created.

In addition to file parameters set during creation, Model 204 maintains a set of parameters that reflect the changing condition of each file. These parameters contain such information as the number of records added and deleted since the file was created, the space used and free space available in the data and index areas, and the number of records in the sorted file overflow areas.

With Model 204 file manager privileges, you can use IFRPRM on an IFSTRT thread to set the following file parameters:

FISTAT
FOPT
FRCVOPT
PRIVDEF
OPENCTL
BRESERVE
DRESERVE

For more information about file parameters, see FPARMS and TABLES file parameters.

CURFILE parameter and the current file

You can also use the IFEPRM call on an IFSTRT thread to get the name of the file last accessed, which is held by the CURFILE parameter.

See HLI: Model 204 files and records for more information about the CURFILE parameter.