Introduction:

VSAM (Virtual Storage Access Method) is a file management system that provides efficient access to large volumes of data on IBM mainframe systems. It offers various options to control the sharing of files among multiple users and programs. One such important feature of VSAM is SHAREOPTIONS, which allows users to specify how files are accessed and shared. In this blog post, we will delve into the concept of SHAREOPTIONS in VSAM, explore how to use them, and understand their significance in mainframe file management.

What are SHAREOPTIONS in VSAM?
SHAREOPTIONS is a parameter associated with VSAM datasets that determines the type and level of file sharing allowed. It is defined during dataset creation and can be modified later if necessary. The SHAREOPTIONS parameter has two components: the share option and the share level.

a) Share Option:
The share option specifies the type of file sharing allowed. It can have one of the following values:

0 (None): No sharing is allowed. The file can only be accessed by one program at a time.
1 (Read): Multiple programs can read the file simultaneously, but no program can write to it.
2 (Update): Multiple programs can read and write to the file simultaneously, but changes made by one program are not immediately visible to other programs.
3 (Exclusive): Only one program can access the file at a time, and no other program can read or write to it.
b) Share Level:
The share level specifies the level of file sharing allowed. It can have one of the following values:

0 (No update): No program can update the file.
1 (Local update): Programs running within the same system can update the file.
2 (Global update): Programs running on different systems can update the file.

How to specify SHAREOPTIONS in VSAM?
To specify SHAREOPTIONS for a VSAM dataset, you need to provide the share option and share level values during dataset creation or modification. This can be done through various methods, including using utility programs or programming languages such as COBOL or Assembler. Let’s explore a few common ways to specify SHAREOPTIONS:

a) Using JCL (Job Control Language):
When creating a VSAM dataset through JCL, you can specify the SHAREOPTIONS parameter within the DD statement for the dataset. For example:

//DD01 DD DSN=MY.VSAM.FILE,
// DISP=(NEW,CATLG),
// SPACE=(CYL,(10,10)),
// DCB=(RECFM=FB,LRECL=80,BLKSIZE=800),
// SHAREOPTIONS(2,1)

The above JCL snippet creates a new VSAM dataset named MY.VSAM.FILE with share option 2 (Update) and share level 1 (Local update).

b) Using COBOL:
In COBOL programs, the SHAREOPTION clause is used in the SELECT statement to specify the share option and level. For example:

SELECT VSAM-FILE
ASSIGN TO MY.VSAM.FILE
ORGANIZATION IS INDEXED
ACCESS MODE IS DYNAMIC
SHAREOPTIONS 2

The SHAREOPTIONS clause in the SELECT statement sets the share option to 2 (Update) for the VSAM file named MY.VSAM.FILE.

The Importance of SHAREOPTIONS in VSAM:
The SHAREOPTIONS parameter plays a vital role in ensuring efficient and controlled access to VSAM datasets. Here are some key reasons why SHAREOPTIONS is significant:

a) Concurrent Access:
By setting appropriate share options, multiple programs can access the same VSAM dataset concurrently. This allows for efficient sharing of data among different applications, resulting in improved system performance and reduced contention for resources.

b) Data Integrity:
SHAREOPTIONS help maintain data integrity by regulating concurrent updates to VSAM datasets. For example, by specifying a share option of 2 (Update), multiple programs can update the file, but changes made by one program are not immediately visible to others. This mechanism prevents conflicts and potential data corruption that may arise from simultaneous updates.

c) Resource Utilization:
SHAREOPTIONS enable efficient utilization of system resources. By allowing concurrent access to files, it reduces idle time and maximizes the utilization of CPU and I/O resources. This is especially crucial in high-volume transaction processing environments where multiple users need simultaneous access to VSAM datasets.

d) Flexibility:
With SHAREOPTIONS, you have the flexibility to tailor the level of file sharing based on your specific requirements. You can choose between read-only access (share option 1), update access (share option 2), or exclusive access (share option 3), depending on the nature of your application and the level of concurrency needed.

Conclusion:

In the realm of VSAM file management, SHAREOPTIONS play a crucial role in determining how datasets are accessed and shared among multiple users and programs. The flexibility provided by SHAREOPTIONS empowers programmers and system administrators to optimize system performance, ensure data integrity, and efficiently utilize system resources. Understanding the different share options and levels enables efficient design and implementation of mainframe applications that rely on VSAM datasets. By leveraging the power of SHAREOPTIONS, organizations can enhance their mainframe systems’ capabilities and streamline their data management processes