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Chapter 4: Configuring CICS Regions

This chapter describes some of the ways in which regions can be used, the information needed to control region processing and how to create and configure regions.

4.1 Overview

On a mainframe, regions are used for a variety of purposes, such as separating departmental applications or projects, and isolating the impact of failures by separating resources into terminal-owning regions, application-owning regions and file-owning regions.

Similarly, on a PC, the use of CICS Option regions varies widely, for example:

4.2 The System Initialization Table (SIT)

The System Initialization Table (SIT) specifies how a region is to be initialized when it starts up. It determines such things as, but is not limited to:

A SIT is defined and stored in a Resource Definition File (RDF). An RDF can hold any number of SITs. You create new SITs with the Project Wizard or with the Resource Definition Facility, which is described in the chapter CICS Resource Definitions in the Administrator's Guide. CICS Option supplies several pre-configured SITs. These can be used as defaults or used as a basis for customizing your own.

Whan you create a new project, you can define the region name, RDF, and SIT that the project is to use. After the project has been created, you can change the region name, RDF, SIT, and startup list with the CICS System Properties dialog box. The changes that you make on the Overrides page of the CICS System Properties dialog box are stored in the project file, not in the RDF.

4.3 The Startup List

The startup list names the resource groups that are to be installed at system initialization. In this way, you can specify which resources are associated with a SIT and therefore which resources are installed when a region is started. You can share resources across multiple regions or you can restrict some resources to a specific region. No matter what resources are defined in an RDF, a resource is not installed for a region unless the group that the resource belongs to is specified in the startup list associated with the SIT used to start the region. (You can, however, use the supplied transaction CINS to install further resource groups once the region is running.)

When you create a project, CICS Option reads the startup list associated with the SIT that you specify from the RDF and stores it in the project file. Any changes that you make to the startup list are not written back to the RDF.

Assume, for example, that the RDF defines the resources shown in Figure 4-1:


Figure 4-1: Example of resources defined in the RDF

Starting a region with the System Initialization Table SAMPSIT1 specified will initialize that region with the two groups SAMPGRP1 and SAMPGRP2. This is because SAMPSIT1 specifies a startup list SAMPLST1 which has only those two groups listed.

Additional groups can be installed to that region when it is running, without having to terminate the region, by using the supplied transaction CINS.

Assuming you have the authority (sign-on security privilege) to run the transaction, enter:

CINS SAMPGRP3

Then the SAMPLIST3 group is installed and made available to region users.

4.4 Recommendations

This section describes some recommended approaches to the setting up of resources to facilitate:

Your system administrator would perform some of the tasks described, while you, as a CICS developer, would perform others.

4.4.1 Group Working

For group working, your system adminstrator should perform the following tasks:

  1. Either:

    • Download the resource definition file you want to use from the mainframe.

    • Create a new resource definition file using the character interface to resource definition.

    For further information on these tasks see the chapter CICS Resource Definitions in the Administrator's Guide

  2. Define a startup list that specifes the resource groups that you want to be available as soon as a CICS region starts. You should base this list on the startup list DFHLIST supplied with Mainframe Express, and add to it the groups supplied with Mainframe Express that start with DFH.

  3. Define a System Initialization Table (SIT) that references the startup list you just created. You would probably want to use the character resource definition utility to perform this task, since it provides many more configuration options than the IDE interface.

  4. Put the resource definition file somewhere on the network where CICS developers can access it from their PCs.

Then, to set up a project that uses this shared resource definition file:

  1. Start the Project Wizard and work your way through the Wizard until you come to the Create new project - CICS resources page.

  2. Click Change and enter the path to the resource definition file, then click Next.

  3. On the Create new project - CICS SIT page, choose the SIT that your system administrator defined in the shared resource definition file, then click Next.

  4. On the Create new project - finish page, click Finish.

Mainframe Express now performs the following actions:

  1. Extracts some configuration settings from the SIT defined in the shared resource definition file, and stores it in the project file (.mvp). These settings are the ones you are most likely to want to change.

  2. Copies the startup list referenced in the SIT from the RDF to the project file (.mvp).

You can now make changes to the SIT and Startup list on your PC without affecting other developers who are using the shared RDF. You can view and change the SIT settings by right-clicking CICS System in the CICS View and clicking Properties. You can make changes to the startup list by right-clicking CICS System in the CICS View and clicking Startup List. You can also add a new resource to the project on your PC without affecting other users. When you add a new resource using the IDE, Mainframe Express by default creates a new resource group with the same name as the project, and adds it to the project's startup list.

When your CICS region is initialized, it obtains the location of the shared RDF from the project file. It reads the SIT specifed in the project file from the RDF, then applies the overrides stored in the project file. It then reads the startup list specifed in the project, not the Startup list stored in the shared RDF.


Notes:

  1. Any changes that you make to the SIT or to the Startup List using the IDE interface are not written back to the shared RDF.

  2. Any changes that are made to the SIT or the Startup list in the shared RDF are not automatically applied to the SIT or Startup list in your project. You can obtain the changes as follows:
    1. Right-click CICS System in the CICS View and click Properties on the popup menu.

    2. On the Settings page click Change.

    3. Click Refresh SIT overrides from RDF on the Change System Properties - SIT page.

    4. Click Load Startup List from RDF on the Change System Properties - Startup List Options page.

    5. Click Finish.

  3. If you want to back up a CICS project, you must include the shared RDF as well as the project file (.mvp) in the backup.

4.4.2 Stand-alone Working

You can set up an RDF for stand-alone working on your own PC as follows:

  1. Start the Project Wizard and work your way through the Wizard until you come to the Create new project - CICS resources page.

  2. Either accept the RDF supplied with Mainframe Express (in folder mfe\config) or click Change and create a new RDF.

  3. On the Create new project - CICS SIT page, either choose a SIT from the existing entries or specify a new SIT.

  4. On the Create new project - finish page, click Finish.

Mainframe Express now performs the following actions:

  1. Either creates a new SIT with default options and a default startup list in the project file (.mvp) or stores the existing SIT that you selected in the project file.

  2. Copies the default Startup list referenced in the SIT from the RDF to the project file (.mvp).

You can make changes to the SIT and the startup list using the IDE. You should only need to use the resource definition character interface if you want to update tables or SIT options that are not accessible via the IDE interface.

4.5 Deferring Loading of PCT Entries

You can control whether to load all PCT entries at startup or to defer the loading of some or all PCT entries until the corresponding transaction ID is entered.

The advantages of loading all PCT entries at startup are:

These advantages are particularly important in a production environment, where you need fast response times and stable region definition. The disadvantage is that if there are many PCT entries to load, the startup time is increased and the shared memory usage will be high.

You can control the loading of PCT entries with the Defer PCT load field of the SIT.

If you defer loading PCT entries, when you enter a transaction ID that is not currently loaded into memory, Mainframe Express searches the groups specified in the original startup list in reverse order. If a PCT entry for the transaction ID is found, it is dynamically loaded into memory for subsequent use. If the transaction ID is not found, a TRANSIDERR occurs as normal.


Note: If a group specified as deferred is empty at startup, it will not be searched subsequently for PCT entries.


The following examples assume that resources are defined as shown.

Example 1

Assume the RDF defines the resources shown in Figure 4-2.


Figure 4-2: Resource Definition File for Example 1

Using DEFSIT1, the following entries are loaded into memory at region startup (in addition to the DFH group entries):

 (TRN2,PROG2) from DEFGRP1
 (TRN3,PROG3) from DEFGRP1
 (TRN4,PROG4) from DEFGRP2
 (TRN1,PROG5) from DEFGRP2


Note: The entry for (TRN1,PROG5) from DEFGRP2 is used instead of the entry for TRN1 in DEFGRP1. This is because DEFGRP2 occurs later than DEFGRP1 in the startup list.


Example 2

Assume the RDF defines the resources shown in Figure 4-3.


Figure 4-3: Resource Definition File for Example 2

Starting the region with DEFSIT2, deferred PCT loading is enabled for all groups in the startup list. No PCT entries are loaded into memory at region startup. When the region is running, if the transaction ID TRN3, for example, is entered from a 3270 terminal, the system will:

 Search DEFGRP2 for a PCT entry=TRN3. Result: Not found
 Search DEFGRP1 for a PCT entry=TRN3. Result: Found. Load the definition into memory    

Subsequent uses of the transaction ID TRN3 will find the PCT entry in memory, so no searching of the resource definition file takes place. Similarly, if the transaction ID TRN1 is entered from a 3270 terminal, the system searches for and finds the definition in DEFGRP2.


Note: This will find the same definition for TRN1 as Example 1.


Example 3

Assume the RDF defines the resources shown in Figure 4-4.


Figure 4-4: Resource Definition File for Example 3

The third type of deferred PCT load allows you to specify the number of groups that will have the loading of their PCT definitions deferred. In this case, the deferred group count is set to 1, so the loading of PCT definitions from DEFGRP2 is deferred.


Note: The number of groups to defer is counted back from the end of the startup list.


In this case, at system startup, the following PCT definitions are loaded into memory:

 (TRN1,PROG1) from DEFGRP1
 (TRN2,PROG2) from DEFGRP1
 (TRN3,PROG3) from DEFGRP1


Note: The definition for transaction ID TRN1 is now taken from DEFGRP1 and not from DEFGRP2, as in Examples 1 and 2.


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