Simultaneous Usage (SU) Mode for VSAM Data Sources in MVS

Principles governing SU mode operations with FOCUS data structures also apply to SU mode with VSAM (VSAM/SU). In VSAM/SU mode, the VSAM data source is allocated to a job called Simultaneous Usage (SU). TSO userids and batch jobs running FOCUS are called source machines. Users on source machines send requests and transactions to the SU address space. VSAM files allocated to SU can only be updated by clients connected to it. Outside of VSAM/SU mode, multiple users can report against VSAM data sources in FOCUS, as well as in other languages, by simply allocating them with DISP=SHR.

In this section:

Starting VSAM/SU Source Machines

Querying the VSAM/SU FOCUS Database Server

No special requirements apply in defining VSAM clusters for SU. Standard efficiency considerations apply to these data sets: SHAREOPTION (l) or (2) is acceptable. Since SU allows only one transaction at a time against the VSAM data source, data integrity is always preserved.

Starting VSAM/SU Source Machines

TSO userids and batch jobs that access VSAM data sources on a FOCUS Database Server can be started with standard FOCUS CLISTs or JCL, with the following changes:

  1. VSAM data sets and paths must not be allocated.

  2. The FOCBMP data set allocated on the FOCUS Database Server must also be allocated on the source machine as well. It can be allocated to any ddname providing flexibility to access more than one FOCUS Database Server at a time.

  3. During the FOCUS session, you must issue a USE command listing the ddnames of each VSAM cluster and path data set to be used during the session. For example:

    4. USE
    VSAM1 ON FOCBMP1
    VSAM2 ON FOCBMP1
    PATH2 ON FOCBMP1
    VSAM9 ON FOCBMP2
    END

    The ddnames of VSAM clusters and path data sets must correspond to those used by SU. Ddnames of the FOCBMP data sets must correspond with those allocated by the client.

    The USE command may be reissued with different parameters at any time during the FOCUS session.

    For applications that only retrieve data, it is preferable not to go through the FOCUS Database Server, so do not issue USE commands for these sources, but allocate them as you would for a TSO user ID in single-user mode.
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Querying the VSAM/SU FOCUS Database Server

To query FOCUS Database Server status, execute the XMISAMT FOCEXEC, selecting the INFO option. XMISAMT is on the FOCUS installation tape in the PDS FICCTL.DATA. Copy it to a central FOCEXEC library during installation.

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