1. Introduction to CICS Transaction Server
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Introduction to CICS Transaction Server
for OS/390 – Unit 2
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2. Unit 2: Managing data and resources
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Unit 2: Managing data and resources
Topics:
2A. Domains and resources
Major domains
The EXEC interface
2B. Resource definition
CICS system definition (CSD)
Terminal definition and management
Structure of a CEDA command
Conserving and sharing resources
2C. Data access and storage
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3. 9/7/2004
Unit 2 contents
The management of system resources is central to the efficiency of the
CICS TS for the OS/390 system. In this unit, you will learn how
resources are organized in CICS TS. You will also become familiar with
the different ways of customizing resource configurations to suit
individual system needs.
This unit also deals with methods of accessing and protecting data, an
important resource in any system.
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4. 9/7/2004
Unit 2 objectives
This is what you should be able to do after completing this unit:
Name the primary method for accessing data sets in CICS
Describe the purpose of a CSD file
List the different methods of defining resources in CICS
Describe the structure of a CEDA command
Explain what sync points and LUWs are
Describe the function of DTB
List the four principles that CICS follows to help ensure data integrity
Describe the functions performed by the CICS API
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5. 2A. Major domains CICS regions are divided into
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2A. Major domains
CICS regions are divided into
several domains, each with its
own set of resources and
functions.
Domains communicate with each
other by means of interfaces
called gates.
The function of a particular domain might be file access, data allocation or data retrieval.
Resources might include transactions, programs, data sets, a terminal or printers.
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2A. Major domains
In Unit 1, you were introduced to a few domains that are involved in
transaction processing: the storage manager, transaction manager,
program manager and dispatcher domains.
CICS also has domains that are responsible for:
Loading application programs (loader domain)
Dispatching CICS messages (message domain)
Interfacing with external security systems (security manager domain)
Two very important domains are the domain manager domain and the
application domain.
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2A. Major domains
The domain manager domain maintains catalogs of important
information about all domains.
The application domain is responsible for terminal management, file
access control, and the interface between CICS and application
programs. The domain contains several key components, such as:
Application and system services
Extended recovery facility (XRF)
Intercommunication segments, such as multiregion operation (MRO) and inter-system communication (ISC)
System control
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8. 9/7/2004
2A. The EXEC interface
Another important component of the application domain is the EXEC
interface program (EIP). The EXEC interface is an application
programming interface (API), a command-level programming interface
intended for CICS execution of any user applications.
Command-level programs issue CICS commands to request services. A
command-level program is easily recognized by the presence of EXEC
CICS commands. Whenever an application program issues an EXEC
CICS command, the EIP takes control and does the following:
Interprets the CICS command
Invokes the relevant control programs to process the request
Acquires or accesses necessary control blocks
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9. 2A. The EXEC interface The EXEC interface block (EIB) is
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2A. The EXEC interface
The EXEC interface block (EIB) is
a control block associated with
each task in this command level.
The EIB contains information useful during the execution of an application, such as time and date of transaction initiation, initiating terminal identification and transaction identification.
The EIB also stores information that is important when using a system dump to debug a program.
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10. 2A. The EXEC interface The basic format for API commands in CICS is:
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2A. The EXEC interface
The basic format for API commands
in CICS is:
EXEC CICS command option(arg)
The command argument is the
operation required, and the optional
option(arg) is a value such as
length(data value) or file(name).
Some of the more common
commands are shown at the right.
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2A. The EXEC interface
When dealing with file access through the API, the command string
includes an identifier for the file that the command is accessing.
For example, if the user were reading a VSAM file, the command might be
EXEC CICS READ FILE(‘payroll’)
followed by more options to further describe the requested operation.
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12. 2A. The EXEC interface CICS API command level is used:
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2A. The EXEC interface
CICS API command level is used:
To initiate communications (through VTAM) with devices such as local or remote terminals. These include printers, workstations, ABMs, and communication links.
To run application programs, including translation arguments, from any resident programming language that is supported by CICS. These languages include PL/I, COBOL, assembler language, C and many others.
To start, monitor, track and enable or disable transactions running on the system, either directly or through other applications, such as database managers.
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13. 2B. CICS system definition
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2B. CICS system definition
One of the main functions of the CICS system is to manage online
resources. Resource definitions are descriptions of the types of
applications and procedures that are used for individual data actions.
Every CICS region has its own set of these resource definitions stored
in a data set called the CICS system definition (CSD).
Resource definitions provide CICS with the information to recognize and
manipulate data appropriately, as well as the information regarding the
properties and interactions between resources. If a resource is not
defined correctly in CICS, it will not be recognized and can cause errors
or transaction failure.
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14. 2B. CICS system definition
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2B. CICS system definition
In CICSPlex architecture, CICS is divided into several regions, and each
region can play a different role in the system. Each region will contain
its own CSD detailing the resources that are used exclusively (or
owned) by that region.
CICS TS for OS/390 is commonly divided into three regions: TOR, AOR
and FOR.
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15. 2B. CICS system definition
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2B. CICS system definition
Terminal owning region (TOR) – Looks after end-user network facilities and needs. The CSD for this region would have definitions for all resources used in terminal sessions, including monitors, printers, and communication devices.
Application owning region (AOR) – Owns user transactions and programs, so its CSD would include definitions for the resources relating to transactions and programs.
File owning region (FOR) – Owns data resources including data files and tables, so its CSD includes definitions for those resources.
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16. 2B. CICS system definition
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2B. CICS system definition
Storage of CICS resource
definitions in CSD is hierarchical.
First, CICS organizes related
resources into named groups.
Then, these groups of resources
are themselves stored in a list that
is installed when CICS TS is
started.
Resource groups are mandatory in CSD; therefore, no resource may be defined without being assigned to a group.
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17. 2B. CICS system definition
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2B. CICS system definition
Resource definition groups should ideally contain no more than 100
definitions. Very large groups, such as those containing network
address definitions, can take a lot of processing time to install when
CICS is started. Similarly, many small groups can slow down processing
time, as well as affect direct access storage device (DASD) space
usage.
It is best to keep group size to a number that can be scrolled through
easily on the screen.
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18. 2B. CICS system definition
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2B. CICS system definition
Generally, the following guidelines can help keep group size at a
reasonable level:
For network-related definitions, sessions must be in the same group as connection definitions. Therefore, a good strategy is to create a group consisting of one connection and its associated sessions.
Terminal definitions should be grouped by department or geographic location.
All definitions pertaining to a particular application should be in one group.
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19. 2B. CICS system definition
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2B. CICS system definition
You will learn about these five methods for resource definition in this
unit:
Resource definition online (RDO) – Uses CICS-supplied transactions (CEDA, CEDB, and CEDC) while a CICS region is running and stores the definitions in the CSD file.
DFHCSDUP offline utility – Operates like RDO, but offline through a batch job.
Automatic installation (Autoinstall) – Works only with user modifications through a definition model. The utility then dynamically creates new definitions based on the model which can prevent the creation of large numbers of definitions.
(continued)
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20. 2B. CICS system definition
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2B. CICS system definition
System programming, through the EXEC CICS CREATE command, creates resources that are independent of the CSD.
Macro definition using assembler macros creates definitions and stores them in assembled tables in a program library. The definitions are installed during CICS initialization.
Of the five listed methods, all are supported by CICS functions.
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21. 2B. CICS system definition
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2B. CICS system definition
RDO is often preferred because it can handle the resource definitions online and it allows fast access.
The advantages of the two methods that employ user modification, EXEC CICS CREATE and autoinstall, are:
They provide user-customized definition.
They enable more efficient management of configuration, installation and storage of resource definitions.
The other two methods, DFHCSDUP and macro, do not allow online installation of definitions. This means that CICS must be modified or restarted for the changes to take effect.
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22. 2B. Terminal definition and management
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2B. Terminal definition and management
The RDO language has keywords for:
Resource types (for example, PROGRAM or TRANSACTION)
Operations on resources (for example, DEFINE or VIEW)
Resource properties (for example, LANGUAGE or DEVICE)
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23. 2B. Terminal definition and management
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2B. Terminal definition and management
There are three major transaction
groups in RDO:
CEDA allows users to modify both
the active CICS system and the CSD.
CEDB allows limited modification of
the CSD (all but INSTALL) and read-
only commands.
CEDC allows only read-only
commands.
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24. 2B. Terminal definition and management
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2B. Terminal definition and management
RDO can control which resources are accessed by which users. This is
done using the CEDA command LOCK, and also through such operator
ID-based security products as RACF.
Most system administrators prevent access to the system terminal
definitions (TYPETERM) and RDO transactions CEDA and CEDB,
among other key resources.
Also, programmer access privileges are often limited to only the
applications that the programmer maintains.
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25. 2B. Using the CEDA commands
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2B. Using the CEDA commands
CEDA commands are used for creating and managing resource
definitions.
A CEDA command begins with a TRANSID, and identifies a resource by
resource type, resource name, group keywords and group name.
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26. 2B. Using the CEDA commands
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2B. Using the CEDA commands
A new resource group is created through a DEFINE command, such as:
CEDA DEFINE PROGRAM(PROG1) GROUP(MYGROUP)
The only other way to create a group name is by specifying it as a TO
group in a COPY command. A group name must be unique, and cannot
be called the same thing as another group or list.
To create a list, use either the ADD command to add a group to a list
(which also creates the new list) or use the APPEND command to add
one list to another (which also creates the new list). Again, list names
must be unique.
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27. 2B. Using the CEDA commands
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2B. Using the CEDA commands
Users can get information about
resources and their definitions in a
few different ways. One is through
the master terminal program. The
TRANSID for the master terminal
program is CEMT.
A CEMT transaction has four
types of commands, as shown to
the right.
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28. 2B. Conserving and sharing resources
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2B. Conserving and sharing resources
Resource definition is vital to the correct operation of CICS systems. If
done incorrectly, or if installed incompletely, many error conditions and
system problems can ensue.
Although the CSD file is usually unique to a particular CICS region,
there are methods of duplicating or sharing definitions with other CICS
regions. There are also flexible methods of list usage within a single-
system CICS setup.
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29. 2B. Conserving and sharing resources
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2B. Conserving and sharing resources
Dual-purpose resource definition allows a
shared CSD file in local and remote CICS
systems. Using this method, the CSD is not
duplicated for different systems but
differentiated by specifying groups of the
CSD that will be used by particular
systems.
For two different CICS regions, one a TOR
and one an AOR, three groups would be
created in a dual-purpose setup: one for the
TOR system, one for the AOR system, and
one that includes resources common to
both systems. One CSD file is used, so disk
storage and maintenance requirements are
reduced.
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30. 2B. Conserving and sharing resources
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2B. Conserving and sharing resources
In a single-system environment,
lists with several different sets of
groups can be installed for
different days of the week,
depending on usage and
workload.
Each time CICS is restarted, a
particular list can be installed that
matches that day’s needs or
activities. This provides resource
definition flexibility for a single-
system CICS setup.
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31. 2B. Conserving and sharing resources
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2B. Conserving and sharing resources
When changing resource lists between systems or within a system, or
when introducing changes to resource definitions, most systems
administrators create a new list. The old list is archived, in case there
are problems and it must be reinstalled in order to return to the
previous resource state. Because the CSD is defined when CICS is
initialized, it is possible to reinitialize CICS and define a different list of
resources if the new list is unworkable.
In large Parallel Sysplex environments that have CICSPlex SM for
OS/390 installed, features like business application services (BAS)
allow resource definition and central system image control across the
entire CICSPlex.
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32. 2B. Terminal definition and management
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2B. Terminal definition and management
CICS needs to know what terminals are connected to the system. With
the CEDA command, the RDO facility is used to identify the VTAM-
supported terminals that operators are using to interact with CICS.
Each terminal receives a resource definition called a terminal control
table terminal entry (TCTTE), which is stored in the CSD.
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33. 2B. Terminal definition and management
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2B. Terminal definition and management
Each TCTTE contains:
A unique 4-character identifier for the terminal
The type of terminal
The terminal status
A pointer to the buffer (TIOA) containing any pending input or output messages
An area reserved for use by CICS during processing
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34. 2B. Terminal definition and management
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2B. Terminal definition and management
If the autoinstall process is used, the TCTTE is built dynamically and is
defined in the CICS region when the user logs on and a VTAM session
is established.
The advantage to this process is that terminals are defined only when in
use. This means that:
Storage space is not used up by idle resources
Startup time is decreased because CICS does not need to build TCTTEs for every terminal
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35. 2B. Terminal definition and management
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2B. Terminal definition and management
When input is received from a
terminal, the message is stored in
a Terminal Input/Out Area (TIOA).
The TIOA is created dynamically by the CICS Terminal Manager module and stores messages exchanged between a terminal and an application program.
The TIOA contains the length of the message, the message itself and a pointer to the TIOA holding the previous message in the dialog.
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36. 2B. Terminal definition and management
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2B. Terminal definition and management
In order to associate each message with the appropriate terminal, the
addresses of a terminal’s TIOAs are stored in the TCTTE for that
terminal. Because transactions are initiated from terminals, transactions also need to be linked to their participating terminals.
To do this, the address of the TCTTE for the initiating terminal is stored
in the TCA that has been set up for the task. Also, the address of the
TCA is stored in the TCTTE of the initiating terminal.
When a message is sent to a terminal, Terminal Management creates a
TIOA to hold the message and transmits it to the terminal.
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37. 9/7/2004
2C. File control
File control is the CICS module responsible for providing access to
data stored in data sets, data tables, and databases.
A CICS application program can access data stored in direct access
data sets as well as the following virtual storage access method
(VSAM) file types:
Entry sequenced data sets (ESDS) – Data is stored in the order in which it is entered.
Key sequenced data sets (KSDS) – The order of data is specified and maintained by an index.
Relative record data sets (RRDS) – Each record is a fixed length and has a numeric ID.
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38. 9/7/2004
2C. File control
Two major CICS components are involved in the file control
process: the file control program (FCP) and the file control table
(FCT).
The FCP consults the FCT for the information necessary to access
application data files. The FCT must contain an entry for each file that a
CICS program accesses. Each FCT entry contains:
The name of the data set
The access method used with the file (for example: VSAM)
The type of access permitted (for example: update, read-only)
Other file attributes, such as the number of tasks CICS will permit to access the file concurrently
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39. 2C. File control When a CICS application program
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2C. File control
When a CICS application program
needs some data, it sends a
request to the FCP by issuing a
CICS file control command.
A file I/O command contains:
The words EXEC CICS (like all CICS commands)
The function (for example, READ)
The file name
The name of the record area in the program’s working storage, and its length
A record identification
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40. 9/7/2004
2C. File control
When retrieving a record, file control needs to acquire storage to hold
it. It does this by calling the storage manager domain.
The performance of applications is improved by requiring that multiple
records from a data set be loaded into a table. Records are then
manipulated within this table, which is kept in main storage, making it
faster for CICS to retrieve the data. CICS ensures that any changes to
the data are recorded in the data set.
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41. 2C. Journaling and logging options
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2C. Journaling and logging options
These file control components are optional with CICS:
Automatic journaling – Writes details of file activity to a specified journal
Automatic logging – Logs file operations (on recoverable files) on the CICS system log and the dynamic log
These can be activated in the file control table at the discretion of the
CICS system administrator. These controls come into play when records
are updated, added to or deleted from a file control data set.
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42. 2C. Journaling and logging options
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2C. Journaling and logging options
The advantage of the automatic
journaling and logging file controls
is that file activity information is
readily available for review in the
event of system failure or backout,
so that file activities and
operations can be easily
duplicated or traced.
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43. 2C. Journaling and logging options
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2C. Journaling and logging options
Other products used with CICS also have journaling and logging
procedures.
One advantage to having another application perform this function in
addition to CICS is that key system information is tracked in more than
one place. Thus, if one application fails, another can be used as backup.
Another advantage is that the different applications can be used to
perform different functions. For instance, with products like File-AID and
Abend-AID, almost any problem application transaction path can be
tracked and analyzed. Some system administrators prefer to use the
enhancement products for error tracking and analysis, freeing the CICS
system for more important tasks.
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2C. Data integrity
Protecting data from accidental loss or corruption is a primary concern
of many businesses. CICS helps ensure the integrity of transaction-related
data by following four key principles in transaction processing, known as
ACID:
Atomicity
Consistency
Isolation
Durability
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45. 9/7/2004
2C. Data integrity
Atomicity – Each transaction is treated as a separate unit. Either the
entire transaction is committed (succeeds), or rolled back (fails). If a
transaction fails, data cannot be corrupted; if it succeeds, the changes
to the database are permanent.
Consistency – A transaction follows established protocols each time it is
run. The transaction uses data in the same way each time, which
prevents data corruption across databases.
Isolation – No two transactions operate simultaneously on the same
data, because CICS keeps tasks independent of one another until
completed.
Durability – Committed data is saved by the system so that, even in
the event of a failure and system restart, processing results are
available.
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2C. Data recovery
Some data is designated a recoverable resource by CICS.
Recoverable resources can include:
Any designated file
Certain transient data and temporary storage queues
Data language/I (DL/I) databases
This data has recovery information logged or recorded by CICS in the
system’s dynamic Log. If a transaction involving a recoverable resource
is successful, then the recovery information is deleted from the log.
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2C. Data recovery
However, if the task fails because of an error (whether in the application
program, data access or transmission, or because of cancellation),
CICS performs dynamic transaction backout (DTB).
This reverses the pre-abend or pre-task failure updates and works
backward from the last change before the failure occurred. DTB keeps
corrupted data from being used by other tasks.
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48. 9/7/2004
2C. Data recovery
DTB functions by using synchronization points (sync points) specified
by application programs.
Sync points are logical points in the program execution and delimit a
logical unit of work (LUW).
A logical unit of work is a logical sequence of processing actions (for
example, database changes) that must be completed before any of the
actions of the sequence can be seen as committed.
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49. 9/7/2004
2C. Data recovery
Sync points occur where the changes being made are consistent and
complete, and can then be committed to the database. After a sync
point is reached:
Held output is sent to its destination
Input is removed from message queues
Database updates are made available to other applications
One task may equal one LUW with no sync point, but most complex
tasks have several sync points.
When there is an abnormal termination, CICS recovery and restart facilities
do not back out program updates before the last completed sync point.
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50. Unit 2 summary In this unit you learned the following:
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Unit 2 summary
In this unit you learned the following:
Two important domains in the CICS system are the domain manager domain and the application domain.
The domain manager domain keeps track of all other domains.
The application domain contains components responsible for terminal management, file access control, and the interface between CICS and application programs.
Command-level programs issue EXEC CICS commands to request services.
(continued)
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51. Unit 2 summary CICS API command level is used:
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Unit 2 summary
CICS API command level is used:
- To initiate communications with devices such as local or remote terminals
- To execute application programs
- To start, monitor, track and enable and disable transactions running on the system
Resource definitions are descriptions of the types of applications and procedures that are used for individual data actions. Every CICS region has its own set of these resource definitions, stored in a data set called the CICS system definition (CSD).
(continued)
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52. 9/7/2004
Unit 2 summary
CICS is commonly divided into three region types, each with its own CSD files:
- Terminal owning region (TOR)
- Application owning region (AOR)
- File owning region (FOR)
CICS organizes related resources into named groups that are further organized into lists.
Of the methods for resource definition, RDO is often preferred because it can handle the resource definitions online and it allows fast access.
(continued)
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53. 9/7/2004
Unit 2 summary
There are three major transaction groups in RDO: CEDA, CEDB, and CEDC. The CEDA group of commands allows the most extensive modification of the active CICS system and the CSD.
File control is the CICS module responsible for providing access to data stored in data sets, data tables and databases.
Two major CICS components are involved in the file control process: the file control program (FCP), and the file control table (FCT).
(continued)
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54. 9/7/2004
Unit 2 summary
CICS helps ensure the integrity of transaction-related data by following four key principles in transaction processing, mnemonically known as ACID: atomicity, consistency, isolation and durability.
To recover a system state after a failure, CICS performs dynamic transaction backout (DTB), which reverses the pre-abend or pre-task failure up to the last sync point.
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