The previous section describes an option how servers of an application
environment can be started. You can allow WLM to manage the number
of servers or you can limit them. This option is applied independently
for each instance of a subsystem. For IBM-supplied subsystems, you
can usually use the default value supplied by the WLM ISPF application.
This section defines subsystem instance as it is used by application
environments and
tells how to select the server start option for IBM-supplied subsystems.
A
subsystem instance for an application environment
is defined as a unique combination of:
- Subsystem type, as specified in the service definition for an application
environment, and
- Subsystem name, as defined by the work manager subsystem when
it connects to workload management.
A subsystem instance using
application
environments has
one of two different scopes, single-system or sysplex, depending on
workload management services
used by its subsystem type.
If the scope is single-system, all the server address spaces for
the subsystem instance are created on the system where the instance
connected to workload management.
If the scope is sysplex, the server spaces can be spread across
the sysplex, with workload management starting
at most one server on each system. The installation may choose to
start additional servers on a system through the START command or
automation, and these servers are equally eligible to accept application
environment work
as the one started automatically.
Note that this scope applies only to application
environment server
management. A subsystem with single-system scope for application
environments, can
still perform sysplex-wide functions for other purposes.
You can specify how the number of servers for a subsystem instance
will be started when defining the
application
environment in
the service definition. Reasons for limiting the number of servers
might be a need to serialize or limit
application
environment server
activity while testing, or a restriction in the subsystem itself.
There are three options how to start servers:
- Managed by WLM
- Limited to a single server address space per system
- Limited to a single server address space per sysplex
Options 1 and 2 apply when the subsystem type supports single-system
scope. Options 1 and 3 apply when the subsystem type supports sysplex
scope.
“Managed by WLM” for single-system scope
means any number of servers may be created for the subsystem instance
on the system where it connected to
workload management.
“Managed
by WLM” for sysplex scope means servers may be created
for the subsystem instance on any number of systems in the sysplex.
The IBM-supplied subsystems using application environments, their
scopes, and valid server limit options are as follows:
Table 1. Application environment server
characteristics| Subsystem type |
Scope |
Valid server limit options |
|---|
| CB |
system |
- 1.) Managed by WLM
-
Use this to address the WLM managed servers. This is the default
for the WebSphere Application Server.
- 2.) Limited to a single server address space per system
-
Use this if you are testing and want to temporarily limit
the number of servers. The WebSphere Application Server itself does
not have a requirement for limiting servers.
|
| DB2® |
system |
- 1.) Managed by WLM
-
Use this to address the WLM managed servers. This is the default
for DB2.
- 2.) Limited to a single server address space per system
-
Use this if the DB2 stored
procedure cannot execute concurrently in multiple address spaces.
This option should be used if a stored procedure is to be run in “debug”
mode and writes to a trace.
|
| IWEB |
system |
- 1.) Managed by WLM
-
Use this to address the WLM managed servers. This is the default
for Internet Connection Server, Domino® Go
Webserver, or IBM® HTTP Server
Powered by Domino (IHS powered by Domino).
- 2.) Limited to a single server address space per system
-
Use this if you are testing and want to temporarily limit
the number of servers. The Internet Connection Server, Domino Go Webserver, or IBM HTTP Server Powered by Domino (IHS powered
by Domino) does not have a requirement for limiting servers.
|
| MQ |
system |
- 1.) Managed by WLM
-
Use this to address the WLM managed servers. This is the default
for MQSeries® Workflow.
- 2.) Limited to a single server address space per system
-
Use this if you are testing and want to temporarily limit
the number of servers. MQSeries Workflow
itself does not have a requirement for limiting servers.
|
| SOM |
sysplex |
- 3.) Limited to a single server address space per sysplex
-
SOMobjects® requires
this limit on the number of servers for an application environment.
This option is enforced by the WLM application.
|
For guidance on deciding which option to use, or to find out what
options are valid for other subsystems that use application
environments, refer
to the subsystem reference information.