Considerations for subsystem configuration for error recovery performance
Each piece of work that runs on the iSeries™ system is called a job. Each job is
a single, identifiable sequence of processing actions that represents a single
use of the system. The basic types of jobs performed are interactive jobs,
batch jobs, spooling jobs, autostart jobs, and prestart jobs.
Jobs that run in subsystems do all work that is performed on the iSeries server. As
the number of users on the system increases, it becomes important for you
to consider how the communications and interactive subsystems should be configured.
The configuration of subsystems has little impact in normal data path
operations. However, multiple subsystems can provide multiple processes to
do cleanup and recovery when error conditions occur. This can result in improved
performance.
As the number of users on the system increases, you must consider the importance
of how subsystems are configured:
- Consider limiting the number of devices that are serviced by a single
subsystem. Between 200 and 300 devices for each subsystem are recommended.
Use the following recommendations to divide these users:
- The number of users in any given subsystem
- The connectivity used to access the system
- The type of work the users do
- The geographic location of the users
- Create additional communications and interactive subsystems to split the
work into multiple subsystems.
- The work that is performed in the QCMN subsystem is for connecting and
disconnecting from the system. Error recovery considerations are important
in the configuration of the communications subsystem.
- To prevent a subsystem from allocating a device, ensure that there are
no workstation or type entries for the devices that you do not want to be
allocated.
- Only use the AT(*ENTER) option if you must allow jobs to transfer into
that subsystem.
- For each subsystem you have defined, you need to identify which users
will run in which subsystems. Use the Add Work Station Entry (ADDWSE) command
and the Remove Work Station Entry (RMVWSE) command. You can set up workstation
entries that identify which devices that subsystem should allocate, as well
as which devices a subsystem should not allocate.
Note:
You can use the ADDWSE commands while the subsystem is active.
However, subsystems do not reallocate device locks dynamically. Eventually,
it might be necessary to end and restart the subsystems to have the device
locks allocated to the choosen subsystem.
To specify the devices a communications subsystem should allocate:
ADDCMNE SBSD(libname/sbsname) DEV(devname*) MODE(modename)
To specify the devices a communications subsystem should
not allocate:
ADDCMNE SBSD(libname/sbsname) DEV(devname*) MODE(modename) MAXACT(0)
Note:
Database and file servers run only in QSERVER when running
over APPC. Do not attempt to allocate sessions running over the QSERVER mode
description. These servers can run over TCP/IP and only then can you run them
in subsystems other than QSERVER.
See the following example for a way of configuring
your communications subsystem.