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IAM/PLEX Introduction

IAM/PLEX Record Level Sharing (Cost option to IAM)

IAM/PLEX provides z/OS SYSPLEX Record Level Sharing (RLS) for IAM datasets across multiple z/OS systems and LPARS that are connected as a z/OS SYSPLEX. The IAM/PLEX product facilitates the sharing at the record level of IAM datasets for multiple concurrently executing CICS/TS regions, batch jobs, and TSO users across a SYSPLEX. To provide these capabilities the IAM/PLEX product utilizes the z/OS SYSPLEX XCF communication services and the SYSPLEX Logger function.

IAM/PLEX RLS is easier to use than VSAM RLS. For CICS/TS, there are no changes required to application programs. The only change required for CICS is to activate a couple of IAM CICS exits for CICS regions using IAM/PLEX RLS. There are no changes needed for input only batch or TSO programs. Batch or TSO programs that perform heavy update processing on recoverable IAM files will need to either utilize the new IAM automatic syncpoint process or revise programs to issue IAM syncpoint calls.

IAM/PLEX is available at an additional cost to the base IAM product. Note that the single system IAM/RLS sharing remains available with the base IAM product and the IAM/AIX option.


An IAM/PLEX address space is started on each z/OS system (or LPAR) that will be sharing IAM files, and is referred to as an IAM/PLEX instance. A unique four character identifier is assigned to each IAM/PLEX instance referred to as the RLSID. Each of these IAM/PLEX instances within a z/OS SYSPLEX is combined into an IAM/PLEX RLS group, which equates to a SYSPLEX XCF group.

Each IAM dataset that is being shared within the IAM/PLEX RLS group is assigned a specific IAM/PLEX instance (RLSID) as the dataset owner. All I/O to any particular IAM dataset will only be processed by the owning IAM/PLEX instance, and are routed to the owning IAM/PLEX using the SYSPLEX XCF services. The record locking is handled by the owning IAM/PLEX instance using internal record locking structures. Journaling is also handled by the owning IAM/PLEX instance utilizing the shared z/OS Sysplex logger.

A user of IAM/PLEX services can be a CICS/TS region, a batch job, a TSO user, or other address space. Each user is directly connected with an IAM/PLEX instance that is executing on the same z/OS system or LPAR. The connection occurs upon opening a shared IAM dataset. Once a user is connected to a specific IAM/PLEX instance, it remains assigned to that specific instance and is not eligible for connection to any other IAM/PLEX instance. The user will be able to access any IAM dataset as permitted by RACF (or other) security that is handled within the IAM/PLEX RLS group that the IAM/PLEX instance is a part of, or any IAM dataset that is not being shared.

Below is diagram of a two system IAM/PLEX. A system is defined as a single z/OS image existing on LPAR or an entire processor. In this diagram, all of the three CICS regions shown (A, B, and C) and the batch job have access to all four IAM datasets (FILE1, FILE2, FILE3, and FILE4). The actual I/O requests for FILE1 and FILE2 are performed under the IAM/PLEX A address space, while the I/O requests for FILE3 and FILE4 are done by the IAM/PLEX B address space. For example, a READ done by CICS-A to FILE3 will be sent by IAM to the IAM/PLEX B address space using Sysplex XCF services, which will subsequently return the record to the CICS-A also through Sysplex XCF services. XCF can be configured to communicate between the two systems using either CTC devices, or using a Sysplex Coupling Facility structure. The shared log services utilize a Sysplex Coupling Facility.

IAM/PLEX New Features


The following features are new for IAM Version 9.0 with IAM/RLS and included as part of the IAM/PLEX product:
  • Optional 64-bit Virtual Storage Use for Lock structures
  • Increases number of record locks that are available
  • Releases 31-bit storage for buffers
  • Optional 64-bit Virtual Storage for Indexes
  • Increases storage available for indexes
  • More files can be opened in IAM/PLEX or IAM/RLS address space
  • Utilizes XTIOT and 31-bit DSAB's
  • More files can be opened in IAM/PLEX or IAM/RLS address space
  • Monitor activity in IAM/PLEX (IAM/RLS) from ISPF (IAMBMON)
  • RLSINFO: New periodic activity report
  • Error messages passed back to user job / address space for easier diagnosis of problems

Steps Needed to Implement IAM/PLEX

Determine desired IAM/PLEX configuration
  • Set up IAM/PLEX procs and parameters for each instance
  • Set up XCF configuration
  • Configure and Define System Logger
  • Install IAM/PLEX CICS Exits
  • Set Dataset Selection Criteria
  • Start IAM/PLEX

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