6. VSAM Dataset Sharing Options Dataset sharing means that a dataset is processed concurrently by more than one user. In VSAM , this sh...
6. VSAM Dataset Sharing Options
Dataset sharing means that a dataset is processed concurrently by more than one user. In VSAM, this sharing feature is controlled by the SHAREOPTIONS parameter in different commands of AMS. The SHAREOPTIONS parameters can have two values. The first value dictates cross-region sharing, i.e., when different programs are running in different address spaces (regions) of the same system. The second value indicates cross-system sharing, i.e., when different programs are running in different address spaces of different systems.
6.1. Cross-Region Sharing
The value of cross-region sharing portion can be 1, 2, 3, 4. The default value is 1.
6.1.1. Share Option 1
The dataset can either be opened for update by one region, or for read-only by multiple regions. This share option provides perfect read and write integrity.
6.1.2. Share Option 2
This share option permits one program to update the dataset, and many other programs to read it at the same time. This provides perfect write integrity, but read integrity is not guaranteed.
6.1.3. Share Option 3
This option allows multiple programs to update and read concurrently. This may cause both write and read integrity problems. Responsibility for maintaining data integrity rests with the application programs.
6.1.4. Share Option 4
This option provides the same features as option 3, but provides better integrity.
6.2. Cross-System Sharing
The value of cross-system sharing can only be 3 or 4.
6.2.1. Share Option 3
When using this option, any number of programs can update or read a file. Maintaining read or write integrity is the user's responsibility. COBOL does not provide any features for maintaining the integrity.
6.2.2. Share Option 4
This option has the same characteristics as share option 3, but provides better integrity.
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