VSAM Components

A component is an individual part of a VSAM dataset. Each component has an entry, a name in the catalog, and an entry in the VTOC. A component can be multi-extent and multi-volume.

VSAM dataset has three components, and those are -

  • Cluster
  • Data component
  • Index component

For example - Assume MATEGJ.TEST.VSAM is the VSAM KSDS file created.

MATEGJ.TEST.VSAM			-	Cluster Component       
MATEGJ.TEST.VSAM.DATA		-	Data Component
MATEGJ.TEST.VSAM.INDEX		-	Index Component
Note! VSAM does not allow JCL concatenation between two VSAM components.

Cluster -

A VSAM cluster is a logical definition for a VSAM dataset and has the below one or two components -

  • The data component contains the data records.
  • The index component of the key-sequenced cluster consists of the index records.

A VSAM cluster is a logical definition for the VSAM dataset of any type (ESDS, KSDS, RRDS, or LDS).

IDCAMS DEFINE CLUSTER access-method services used to define VSAM datasets (clusters) with data and index components. This process includes creating an entry in an integrated catalog without any data transfer.

The below information is mandatory to create the dataset -

  • Name of the dataset.
  • Name of the catalog to contain this definition.
  • Organization (sequential, indexed, or relative).
  • Device and volumes that the dataset occupy.
  • Space required for the dataset.
  • Record size and control interval sizes (CISIZE).

For example - Assume MATEGJ.TEST.VSAM is the VSAM KSDS file created.

MATEGJ.TEST.VSAM			-	Cluster Component

Data Component -

  • VSAM Data Component contains data records. These data records can be small or large that might spread across CIs and CA.
  • Every VSAM file type (ESDS, KSDS, RRDS, VRRDS, LDS) has a data component. KSDS and vRRDS only have the index component.
  • The data component is part of the VSAM dataset, alternate index, or catalog.

For example - Assume MATEGJ.TEST.VSAM is the VSAM KSDS file created.

MATEGJ.TEST.VSAM 
MATEGJ.TEST.VSAM.DATA		-	Data Component

Index Component -

  • The index component contains index records with the key fields/RBA of data records.
  • The key fields are a collection of the single or multiple fields from the logical data record.
  • VSAM can randomly retrieve the record from the data component using the index.

For example - Assume MATEGJ.TEST.VSAM is the VSAM KSDS file created.

MATEGJ.TEST.VSAM
MATEGJ.TEST.VSAM.DATA
MATEGJ.TEST.VSAM.INDEX		-	Index Component

Component Example