Relative record number (RRN), relative byte address (RBA) and extended relative byte address (XRBA)

RRN

RRN specifies that the record identification field contains the relative record number of the record to be accessed. The first record in the data set is number one. All file control commands that refer to an RRDS, and specify the RIDFLD option, must also specify the RRN option.

RBA and XRBA

RBA specifies that the record identification field contains the relative byte address of the record to be accessed. A relative byte address is used to access an ESDS, and it can also be used to access a KSDS that is not opened in RLS access mode. All file control commands that refer to an ESDS base, and specify the RIDFLD option, must also specify the RBA option.

An RBA is an unsigned 32 bit number. The use of a 32 bit RBA means that a standard ESDS cannot contain more than 4 GB of data. However, there is a different ESDS that supports 64 bit extended relative byte addresses (XRBAs) and which is therefore not subject to the 4 GB limit. We call this type of ESDS an extended ESDS. From CICS® TS for z/OS®, Version 3.2 onwards, CICS supports 64 bit XRBAs and extended ESDS data sets.

Normally, to access an extended ESDS a program supplies a 64 bit XRBA. You can convert existing programs that use a 32 bit RBA to use a 64 bit XRBA, by replacing the RBA keyword on the relevant commands with the XRBA keyword and changing the lengths of the areas used for keys. Also in some circumstances it is possible to reuse older programs without change to access an extended ESDS, if they pass 32 bit RBAs but do not use them. Upgrading to extended addressing for ESDS explains how to upgrade a standard ESDS to an extended addressing ESDS, and how to upgrade or reuse your existing programs with the new format.