Here are some common questions and answers about the VSAM alternate index.
VSAM Alternate Index
1. What is an alternate index?
An alternate index in VSAM is an additional access path to a VSAM data set that allows records to be retrieved by a Key other than the primary key. It provides an alternative way of accessing data stored in a VSAM data set, allowing for more flexible and efficient data retrieval. VSAM -Alternate index only allowed on KSDS and ESDS, but not on RRDS
2. Why do you need an alternate index?
Declaring an alternate index needed for an alternate key and a Path. An alternate key is different from the alternate index. The Path behaves by accessing records from the cluster.
3. What is the Path?
The Path is for an alternate Index and the base for the main cluster.
4. When do you update the alternate index?
When you update a record by its path, the alternate index is automatically updated.
5. How to define alternate index in CICS applications?
You can use an alternate index to access records from files in CICS. This means that instead of retrieving file data, the program retrieves index data. However, please note that this operation is not supported for files opened in record-level sharing (RLS) mode.
6. How is an alternate index created in VSAM?
To create an alternate index in VSAM, you must define an AMS (Alternate Index Structure) for the VSAM data set. The AMS specifies the alternate key and the location where the index is stored. Then, using the IDCAMS utility, you can define and load the AMS to create the alternate index structure.
7. What are the benefits of using an alternate index?
- Improved performance: Alternate indexes allow faster access to specific records by using a different key, eliminating the need to search the entire data set.
- Data organization: Alternate indexes can be used to organize data in a different order than the primary key, providing different sorting and grouping options.
- Increased flexibility: With alternate indexes, you can access the same data set using multiple keys, enabling various queries and searches.
8. Can multiple alternate indexes be created for a single VSAM data set?
Yes, possible. You can create multiple alternate indexes for a single VSAM data set. Each alternate index is defined with its unique key, providing different ways to access the data stored in the VSAM data set.
9. How are records accessed using an alternate index in VSAM?
To access records using an alternate index in VSAM. You specify the key value associated with the alternate index in your program or query. The VSAM system will use the alternate index structure to locate the corresponding subset of records and retrieve the requested data efficiently.
Conclusion
I hope this provides the information you were looking for! Let me know if you have any further questions.
Srinimf 
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