z/OS V1R6.0 DFSMS Access Method Services for Catalogs

DEFINE ALTERNATEINDEXWhen you use BLDINDEX to build a reusable alternate index, thehigh-used RBA is always reset to zero when the alternate index is openedfor BLDINDEX processing.Reusable alternate indexes can be multivolumed and might have up to 123physical extents.Exception: If you use the keyword UNIQUE with REUSE, the DEFINEcommand is unsuccessful.Abbreviation: RUSNOREUSESpecifies that the alternate index cannot be used again as a new alternateindex.Abbreviation: NRUSSHAREOPTIONS(crossregion[ crosssystem]|1 3)Specifies how an alternate index’s data or index component can be sharedamong users. However, SMS-managed volumes, and catalogs containingSMS-managed data sets, must not be shared with non-SMS systems. For dataintegrity, ensure that share options defined for data and index components arethe same. For a description of data set sharing, see z/OS DFSMS: Using DataSets.crossregionIndicates the amount of sharing allowed among regions within the samesystem or within multiple systems using global resource serialization(GRS). Independent job steps in an operating system, or multiple systemsin a GRS ring, can access a VSAM data set concurrently. For moreinformation about GRS, see z/OS MVS Planning: Global ResourceSerialization. To share a data set, each user must include DISP=SHR in thedata set’s DD statement. You can use the following options:OPT 1 The data set can be shared by any number of users for readprocessing, or the data set can be accessed by only one user forread and write processing. This setting does not allow anynon-RLS access when the data set is already open for VSAM RLSor DFSMStvs processing. An RLS or DFSMStvs open fails with thisoption if the data set is already open for any processing.OPT 2 The data set can be accessed by any number of users for readprocessing, and it can also be accessed by one user for writeprocessing. It is the user’s responsibility to provide read integrity.VSAM ensures write integrity by obtaining exclusive control for acontrol interval while it is being updated. A VSAM RLS orDFSMStvs open is not allowed while the data set is open fornon-RLS output.If the data set has already been opened for VSAM RLS orDFSMStvs processing, a non-RLS open for input is allowed; anon-RLS open for output fails. If the data set is opened for input innon-RLS mode, a VSAM RLS or DFSMStvs open is allowed.OPT 3 The data set can be fully shared by any number of users. The useris responsible for maintaining both read and write integrity for thedata the program accesses. This setting does not allow anynon-RLS access when the data set is already open for VSAM RLSor DFSMStvs processing. If the data set is opened for input innon-RLS mode, a VSAM RLS or DFSMStvs open is allowed.Chapter 13. DEFINE ALTERNATEINDEX 137