VSAM: What info can we gather from the first 5 bytes of Alternate Index on KSDS ?

First of all, to view the control bytes, open the alt. index in edit mode. Put “hex on”

Following are the information available in the control bytes:

First Byte:

00 = Base is KSDS and has Unique Alt. key value

01 = Base is KSDS and has duplicate Alt. key value

80 = Base is ESDS and has Unique Alt. key value

81 = Base is ESDS and has duplicate Alt. key value

Second Byte:

It gives the length of Primary key length

Third & Fourth Byte:

It gives the number of Primary keys associated with alt. key

Fifth Byte:

It has the alt. key length

Hence,

Logical record length = 5 + value in byte 5 + value in byte 2 * value in bytes 3 & 4