RRDS
A relative record dataset: a VSAM dataset of numbered slots, where each record is found by its slot number.
Also written relative record dataset, NUMBERED, VRRDS, LDS, linear dataset
An RRDS, or relative record dataset, is a VSAM dataset made of numbered slots. Record 1 goes in slot 1, record 2 in slot 2, and so on. A program reads or writes a record by giving its slot number, called the relative record number, without any key.
Slots can be empty, and a record can be added to any free slot or deleted from it. In a normal RRDS every slot is the same size, so all records have a fixed length. A variant, the VRRDS, allows records of different lengths. An RRDS is defined with IDCAMS using the NUMBERED option.
It fits data where the position is the natural way to find a record, such as a table of branch codes numbered 1 to 500. It is less common than a KSDS.
A fourth VSAM type is the linear dataset, or LDS. It has no records at all, just a stream of bytes in 4 KB pages. Programs rarely use it directly, but DB2 table spaces and zFS file systems are stored in linear datasets.
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- VSAMA family of dataset types built for fast record access by key, used where applications need to look records up rather than read them in order.
- KSDSThe most common VSAM dataset type, where every record has a unique key used to find it directly.
- ESDSAn entry-sequenced dataset: a VSAM dataset where records are kept in the order they were added, with no key.
- IDCAMSThe utility used to create, list, copy and delete datasets, and the standard tool for anything involving VSAM.
- zFSThe z/OS File System: the type of file system that holds Unix files and directories on z/OS.
- Table spaceThe storage structure in DB2 for z/OS that holds the data of one or more tables, kept in VSAM datasets that DB2 manages.