Using the ALLOCATE subcommand to customize dynamically defined areas

If you elect to dynamically define the areas for the INITIALIZE command, you can specify unique allocation characteristics for the areas by using the ALLOCATE subcommand and its related keywords.

The ALLOCATE subcommand can be used as a replacement for DELETE, DEFINE, and other statements that are normally specified by executing the Access Method Services IDCAMS program.

Note

If the IDCAMS program is already defined in your job input, it is not necessary to remove it. However, any defining statements that are specified under IDCAMS for the area are superseded by similar parameters that are specified on the ALLOCATE subcommand.

By applying the functionality available with the ALLOCATE subcommand, you can accomplish the following tasks and performance improvements:

Automatically adjust the VSAM cluster definition to match an area’s size characteristics
Help to simplify JCL streams and job restarts by combining VSAM cluster definition (traditionally defined by IDCAMS) and area processing into a single step
Improve the area’s usage of fragmented DASD space and irregular sized extents
Enhance system I/O performance by promoting parallel processing against the area by easily separating the RAA, IOVF, and SDEP portions of an area across multiple volumes

The ALLOCATE subcommand lets you perform the following tasks:

Delete/define, reuse, or rename the VSAM cluster that is used for the areas
Pass a sequential or partitioned data set to Access Method Services to be used as input for allocation of the new VSAM cluster
Specify the number of volumes and allocation units for the areas
Specify the number of volumes and allocation units for the RAA, IOVF, and SDEP portions of the areas
Pass optional parameters to Access Method Services for the VSAM cluster definition
Specify the SMS storage class, management class, and data class for the areas
Specify space requirements for the areas
Specify volume serial identifiers for the areas

These functions are defined by specifying combinations of keywords that are specified on the ALLOCATE subcommand.

Identifying the areas for ALLOCATE processing

The OAREA keyword is specified on the ALLOCATE subcommand to identify the areas for which you want to customize allocation. You can specify one or more areas on a single ALLOCATE subcommand, or specify separate ALLOCATE subcommands for any (or all) of the areas that are identified on the INITIALIZE command’s IAREA keyword.

Areas can be specified on the OAREA keyword under the ALLOCATE subcommand by using any combination of area names, area numbers, or area ranges. Available parameters for the OAREA keyword under the ALLOCATE subcommand are the same as those for the IAREA keyword as specified under the INITIALIZE command. For more information, see Selecting-the-Database-and-Areas-for-Initializing-a-DEDB.

Specifying the area to be used

The ACTUATE keyword requests optional VSAM cluster processing.

The following parameters are available:

ACTUATE=DELETE causes the current VSAM cluster to be deleted before the new VSAM cluster is allocated.
ACTUATE=REUSE causes the current VSAM cluster to be allocated and overwritten without allocating a new VSAM cluster.
ACTUATE=RENAME causes the current VSAM cluster name to be altered according to the data set name mask that you specify before allocating the new VSAM cluster.
ACTUATE=IDCAMS causes a sequential or partitioned data set to be passed to Access Method Services as input for the allocation of the new VSAM cluster. Due to the design of this feature, each area should have a separate IDCAMS definition.

If you omit the ACTUATE keyword, it is assumed that the area does not already exist. A new area will be allocated.

You can also specify the EROPT parameter on the ACTUATE keyword to specify whether ALLOCATE subcommand processing should continue if a processing error is encountered. Specify EROPT=IGNORE to continue processing. Specify EROPT=ABORT to terminate processing.

Allocating the area and specific portions of the area

Four keywords are available on the ALLOCATE subcommand that control the following allocation characteristics for the specified area or portion of the area:

Size of each extent for the area or portion of the area
Number of extents (volumes) that the area or portion of the area will span

By default, the entire area or any portions of an area (RAA, IOVF or SDEP) that are not explicitly specified with extent size or volume count parameters will be contained on one volume.

The size of the extents are controlled by specifying one or more values on the keywords:

The CONFIGURE_AREA keyword is used to specify the size of the extent or extents for the entire area data set.
The CONFIGURE_RAA keyword specifies the size of the extent or extents for the root addressable portion of the area data set.
The CONFIGURE_IOVF keyword specifies the size of the extent or extents for the independent overflow portion of the area data set.
The CONFIGURE_SDEP keyword specifies the size of the extent or extents for the sequential dependent portion of the area data set.

The values that are specified on the CONFIGURE_AREA keyword or any combination of the CONFIGURE_RAA, CONFIGURE_IOVF, and CONFIGURE_SDEP keywords represent the amount of track or cylinder space to be allocated to the extent. Selection of tracks or cylinders for the extents is requested by specifying the SPACE keyword parameter on the ALLOCATE subcommand or is determined by IDCAMS.

To define multiple extents with the same amount of space, you can specify a value on the VOLCNT parameter with an extent size value. The value that is specified on the VOLCNT parameter indicates the number of extents (volumes) that the area or portion of the area will span. Each extent is sized according to the specified extent size.

You can specify the IDCAMS_OPTION keyword on the ALLOCATE subcommand to pass optional parameters to Access Method Services for the VSAM cluster definition. Numerous parameters are available for use with this keyword to control the values that are used by AMS for the VSAM cluster definition. For more information, see the IBM Access Method Services Reference Manual.

Specifying space requirements class and volume identifier for the area

Other keywords are available that let you specify the SMS class, space requirements, and volume serial identifier for the area. These keywords function in the same manner as on other Fast Path/EP subcommands. These include the AVGREC, DATACLAS, MGMTCLAS, SPACE, STORCLAS and VOLSER keywords.