Defining a VSO DEDB area

All of the Virtual Storage Option (VSO) information for a DEDB is recorded in the RECON data set.

Use the following parameters of the DBRC INIT.DBDS and CHANGE.DBDS commands to define your VSO DEDB Areas:

VSO

Defines the area as a VSO area.

When a CI is read for the first time, it will be copied into a z/OS® data space or a coupling facility structure. Data is read into a common buffer and is then copied into the data space or structure. Subsequent access to the data retrieves it from the data space or structure rather than from DASD.

CIs that are not read are not copied into the data space or structure.

All updates to the data are copied back to the data space or structure and any locks held are released. Updated CIs are periodically written back to DASD.

NOVSO

Defines the area as a non-VSO area. This is the default.

You can use NOVSO to define a DEDB as non-VSO or to turn off the VSO option for a given area. If the area is in virtual storage when it is redefined as NOVSO, the area must be stopped (/STOP AREA or /DBR AREA) or removed from virtual storage (/VUNLOAD) for the change to take effect.

PRELOAD

For VSO areas, this preloads the area into the data space or coupling facility structure when the VSO area is opened. This keyword implies the PREOPEN keyword, thus if PRELOAD is specified, then PREOPEN does not have to be specified.

The root addressable portion and the independent overflow portion of an area are loaded into the data space or coupling facility structure at control region initialization or during /START AREA processing. Data is then read from the data space or coupling facility structure to a common buffer. Updates are copied back to the data space or coupling facility structure and any locks are released. Updated CIs are periodically written back to DASD.

NOPREL

Defines the area as load-on-demand. For VSO DEDBs areas, as CIs are read from the data set, they are copied to the data space or coupling facility structure. This is the default.

To define an area with NOPREL gives you the ability to deactivate the preload processing. The area is not preloaded into the data space or coupling facility structure the next time that it is opened.

If you specify NOPREL, and you want the area to be preopened, you must separately specify PREOPEN for the area.

CFSTR1

Defines the name of the cache structure in the primary coupling facility. Cache structure names must follow z/OS coupling facility naming conventions. CFSTR1 uses the name of the DEDB area as its default. This parameter is valid only for VSO DEDB areas that are defined with SHARELVL(2|3).

CFSTR2

Defines the secondary coupling facility cache structure name when you use IMS-managed duplexing of structures. The cache structure name must follow z/OS coupling facility naming conventions. CFSTR2 does not provide a default name. This parameter is valid only for VSO areas of DEDBs that are defined with SHARELVL(2|3) and that are single-area structures. This parameter cannot be used with multi-area structures, which use system-managed duplexing.

MAS

Defines a VSO DEDB area as using a multi-area structure as opposed to a single-area structure.

NOMAS

Defines a VSO DEDB area as using a single-area cache structure as opposed to a multi-area structure. NOMAS is the default.

LKASID | NOLKASID

Specifies whether buffer lookaside is performed on read requests for this area.

NOLKASID

Indicates that buffer lookaside is not performed on read requests for this area. NOLKASID is the default.

LKASID

Indicates that buffer lookaside is performed on read requests for this area.

For VSO DEDB areas that use a single-area structure, this parameter is required. The value that is defined in the RECON data set for the area takes precedence over the value defined in the DFSVSMxx PROCLIB member.

For VSO DEDB areas that use a multi-area structure, LKASID or NOLKASID must be specified by using the DFSVSMxx PROCLIB member. Specifications in the RECON data set are ignored.

FULLSEG | NOFULLSG

FULLSEG

Indicates that the full segment image is to be logged.

NOFULLSG

Indicates that only the updated portion of a segment is to be logged.

If neither of these keywords is specified, the default value set in the database record for the DEDB is used.