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

DEFINE CLUSTERintegrity. VSAM ensures write integrity by obtaining exclusivecontrol for a control interval while it is being updated. AVSAM RLS or DFSMStvs open is not allowed while the dataset is open for non-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 forinput in non-RLS mode, a VSAM RLS or DFSMStvs open isallowed.OPT 3 The data set can be fully shared by any number of users. Eachuser is responsible for maintaining both read and writeintegrity for the data the program accesses. This setting doesnot allow any non-RLS access when the data set is alreadyopen for VSAM RLS or DFSMStvs processing. If the data set isopened for input in non-RLS mode, a VSAM RLS or DFSMStvsopen is allowed.OPT 4 The data set can be fully shared by any number of users. Foreach request, VSAM refreshes the buffers used for directprocessing. This setting does not allow any non-RLS accesswhen the data set is already open for VSAM RLS or DFSMStvsprocessing. If the data set is opened for input in non-RLSmode, a VSAM RLS or DFSMStvs open is allowed.As in SHAREOPTIONS 3, each user is responsible formaintaining both read and write integrity for the data theprogram accesses.crosssystemSpecifies the amount of sharing allowed among systems. Job steps of twoor more operating systems can gain access to the same VSAM data setregardless of the disposition indicated in each step’s DD statement for thedata set. However, if you are using GRS across systems or JES3, the dataset might not be shared depending on the disposition of the system.To get exclusive control of the data set’s volume, a task in one systemissues the RESERVE macro. The level of cross-system sharing allowed byVSAM applies only in a multiple operating system environment.The cross-system sharing options are ignored by RLS or DFSMStvsprocessing. The values are:1 Reserved2 Reserved3 Specifies that the data set can be fully shared. With this option,each user is responsible for maintaining both read and writeintegrity for the data that user’s program accesses. Userprograms that ignore write integrity guidelines can causeVSAM program checks, uncorrectable data set errors, and otherunpredictable results. This option requires each user to beresponsible for maintenance. The RESERVE and DEQ macrosare required with this option to maintain data set integrity. (Forinformation on using RESERVE and DEQ, see z/OS MVSChapter 14. DEFINE CLUSTER 163