1. What is the difference between ESDS and Seq file when we are accessing a records in sequential?
ESDS is a sequential file reading only
2. What is VSAM return code 29, 21, 10?
21 - A sequence error exists for a sequentially accessed indexed file. The prime record key value has been changed by the program between the successful execution of a READ statement and the execution of the next REWRITE statement for that file, or the ascending requirements for successive record key values were violated.
10 - A sequential READ statement was attempted and no next logical record existed in the file because the end of the file had been reached, or the first READ was attempted on an optional input file that was not present.
What is the difference between ESDS and Seq file when we are accessing a records in sequential?
The ESDS is similar to Sequencial file. When it come to record accessing, the records are fetched in the same way as the Seq datasets but ESDS has more flexiblity than Seq datasets. In ESDS the records are fetched witha Relative Byte Address (RBA).
With RBA random access of records is possible.
Records can be updated/overwritten in ESDS , these records need not be of the same length.