IBM VSAM Frequently Asked Interview Questions and Answers

8/16/2009 No Comment

VSAM Frequently Asked Interview Questions and Answers.

Explain what is is an alternate index in VSAM?
Answer : An alternate index in VSAM is another file related to the cluster, but sorted using an alternate key that can have duplicates.

Explain the process of creating an alternate index?
Answer : You use the IDCAMS utility with the DEFINE AIX option after you build the cluster and then do another IDCAMS with the BLDINDEX option to populate the alternate index.

Can you tell me what is the parameter in the DEFINE AIX option that is used to determine the maximum number of duplicate keys allowable?

Answer : We can use the RECORDSIZE parameter to determine it. There are 2 numbers that follow this: the 1st is the average and the 2nd is the maximum. The values are equal to 5 + (cluster key length) + N*(alternate key length), where N is the allowable number of duplicates.

Can you name a few common VSAM status codes.

  • 00-OK
  • 02-READ a duplicate alternate key
  • 10-end of file reached while doing a READ
  • 22-trying to WRITE a duplicate primary key
  • 23-record not found while doing a READ
  • 97-file integrity verified, do an IDCAMS VERIFY
Explain what do you meany by buffering and how does it apply to VSAM files.
Answer : When  there are large blocks of data that are to be used, more main storage is required than when smaller blocks are used, but one advantage of large blocks is that it save CPU time and disk space. Morever, extra buffers may save elapsed time since the program does not have to wait for an I/O to complete for it to continue processing.

In JCL, you specify BUFNI (number of index buffers) and BUFND (number of data buffers) as sub parameters of the AMP parameter.

  • For random access, the BUFNI is one more than the number of index levels and a BUFND of 2 is fine.
  • For sequential access, a BUFNI of 1 and a minimum of 5 for BUFND is fine.
  • For dynamic access, the values of each is the higher of the numbers for either random or sequential.
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