2.17 WLM Multisystem Enclaves Structure
This section contains information related to the following:
Usage of WLM Enclaves structures
Sizing of WLM Enclaves structures
Placement of WLM Enclaves structures
WLM Enclaves structure rebuild characteristics
WLM Enclaves structures and volatility
2.17.1 WLM Enclaves Structure Usage
MVS/ESA SP 5.2.0 introduced the ability to create an enclave and to schedule
SRBs into it. OS/390 R3 added the ability to create a dependent enclave which
represents an extension of an existing transaction, and to join TCBs to enclaves.
OS/390 V2R9 adds the ability to extend the scope of an enclave to include SRBs
and TCBs running on multiple MVS images in a Parallel Sysplex.
Some work managers split large transactions across multiple systems in a
parallel sysplex, improving the transaction's overall response time. These work
managers can use multisystem enclaves to provide consistent management and
reporting for these types of transactions.
WLM uses a CF cache structure to maintain information about each of the
components of the multisystem enclaves.
WLM Multisystem Enclaves requires OS/390 V2R9, CFLEVEL=9, and a CFRM
CDS that has been formatted with the ITEMS(SMREBLD) option, meaning that
systems in the Parallel Sysplex must be on OS/390 V2R8 or higher.
2.17.2 WLM Enclaves Structure Sizing
It may be difficult to size the SYSZWLM_WORKUNIT structure at first, as there is
no sure way to know exactly how many parallel units-of-work may exist at any
given time. The best option is take a best guess at the initial and maximum
sizes and then alter the structure size based on performance and/or change in
If the structure's maximum size is defined too low, work managers will
experience failures when they try to export enclaves. It is the work manager's
responsibility to respond to such a failure. The work requests may instead be
run locally (increasing the response time), or the work requests may fail.
At the time of writing, it is planned to add support for WLM Multisystem Enclaves
to the CF Sizer. In the interim, information to help you size the WLM
Multisystem Enclaves structure is available in
OS/390 MVS Planning: Workload
2.17.3 WLM Enclaves Structure Placement
There are no specific considerations in relation to placement of the WLM
Multisystem Enclaves structure.
Parallel Sysplex Configuration, Volume 2: Cookbook