VSAM Interview Questions and Answers - DoAnswers.com

Virtual Storage Access Method (VSAM) is an IBM disk file storage scheme first used in the OS/VS2 operating system and later used throughout the MVS architecture. VSAM comprises four access methods: Key Sequenced Data Set (KSDS), Relative Record Data Set (RRDS), Entry Sequenced Data Set (ESDS) and Linear Data Set (LDS). See record-oriented filesystem. VSAM records can be of fixed or variable length. They are organised in fixed-size blocks called Control Intervals (CIs), and then into larger divisions called Control Areas (CAs). Control Interval sizes are measured in bytes � e.g. 4K � while Control Area sizes are measured in disk tracks or cylinders. Virtual Storage Access Method (VSAM) is an IBM disk file storage scheme first used in the OS/VS2 operating system and later used throughout the MVS architecture. VSAM comprises four access methods: Key Sequenced Data Set (KSDS), Relative Record Data Set (RRDS), Entry Sequenced Data Set (ESDS) and Linear Data Set (LDS). See record-oriented filesystem. VSAM records can be of fixed or variable length. They are organised in fixed-size blocks called Control Intervals (CIs), and then into larger divisions called Control Areas (CAs). Control Interval sizes are measured in bytes � e.g. 4K � while Control Area sizes are measured in disk tracks or cylinders. Virtual Storage Access Method (VSAM) is an IBM disk file storage scheme first used in the OS/VS2 operating system and later used throughout the MVS architecture. VSAM comprises four access methods: Key Sequenced Data Set (KSDS), Relative Record Data Set (RRDS), Entry Sequenced Data Set (ESDS) and Linear Data Set (LDS). See record-oriented filesystem. VSAM records can be of fixed or variable length. They are organised in fixed-size blocks called Control Intervals (CIs), and then into larger divisions called Control Areas (CAs). Control Interval sizes are measured in bytes � e.g. 4K � while Control Area sizes are measured in disk tracks or cylinders.

VSAM Interviews are getting tough these days as the technology grows faster. To get through the VSAM interview one needs to update him/herself in a regular manner. Having said that, just before the interview, it is very important to have a quick glance of the reputed VSAM questions and answers to make yourself comfortable during the interview process. This is where DoAnswers.com helps you in renewing yourself on VSAM and various other technologies interview preparation.

1. Assuming that the DEFINE JCL is not available, how do you get info about a VSAM file's organisation?

It defines the cross-region and cross-system sharing capabilities of the dataset. Syntax is SHR(Crvalue, CSvalue) value 1 means multiple read OR single write (read integrity) 2 means multiple read AND single write (Write integrity) 3 means Multiple read AND multiple write 4 is same as 3, which refreshes the buffer with every random access. default is SHR(1 3).

No, the DCB of the model dataset can be overridden when you allocate new versions.

5. Do primary key values have to be unique? Do alternate key values have to be unique?

6. During processing of a VSAM file, some system error occurs and it is subsequently unusable . What do you do ?

Control information consists of RDF (Record Descriptor Field) and CIDF (Control Interval Descriptor Field). Every CI contains one CIDF which is a field consisting of the last 4 bytes of a CI. It contains information about the offset and the length of free space in the CI. In case of fixed size records each CI contains two RDF's and each RDF is 3 bytes in length. In case of the variable size records,there is a separate RDF for each record in the CI. The size of the Data portion of the CI should be multiple of 512 bytes or 2,048 bytes. Max size of the CI is 32K. The size of the index portion of CI could be one of the following: 512, 1024, 2048, 4096.

The START command is used read other than the next VSAM record. A value must be moved into the RECORD KEY. The KEY clause is optional, but it can be used to specify a relational (equal, less than, etc.) operator.

base-file-name.GnnnnnV00 where nnnn= generation number (upto 255). nnnn will be 0000 for the 1st generation.

They are stored without respect to the contents of the records and in the order in which they are included in the file.