Specifying VSAM and OSAM subpools

Use control statements in the DFSVSAMP data set or the DFSVSMxx member of the IMS PROCLIB data set to specify VSAM and OSAM subpools.

The following example shows the control statements to construct a single OSAM subpool with four 2 KB buffers each and two VSAM subpools. The first subpool contains four 2048-byte buffers, and the second subpool contains fifteen 1024-byte buffers. The new KSDS records use mass insert.

IOBF=(2K,4,N,N)
VSRBF=2048,4
VSRBF=1024,15
OPTIONS,INSERT=SEQ

For information about specifying these control statements, see DFSVSMxx member of the IMS PROCLIB data set.

For IMS batch environments, the //DFSVSAMP data set provides the control statements listed in the example. Additionally, the //DFSVSAMP data set provides the GTF trace option. GTF trace records reflect the stream of I/O requests to the OSAM buffer handler.

In an IMS environment, the DFSVSMxx member of the IMS PROCLIB data set provides the statements. Do not place DFSVSAMP in the same PDS as your user application files. This causes an ABEND0C4 in DFSRTM00. For more information about GTF trace records, refer to IMS Version 15 System Administration.

Dynamic database buffer pool definition

In addition to defining OSAM and VSAM subpools in the DFSVSMxx member of the IMS PROCLIB data set, OSAM and VSAM subpools can be changed dynamically, while IMS resources are actively in use. Define database buffer pool definitions dynamically by specifying parameters in the DFSDFxxx member of the IMS PROCLIB data set and then issuing a type-2 UPDATE POOL TYPE(DBAS) command.

The DFSDFxxx buffer pool values that are brought online dynamically take the place of the values specified in the DFSVSMxxx member. However, the DFSDFxxx member is not read for subpool definitions during IMS startup. The changes made to the DFSDFxxx member are processed only for dynamic changes initiated by the UPDATE POOL TYPE(DBAS) command. The DFSVSMxx member must contain subpool definitions for IMS startup.