Running application servers on your z/OS® system
often requires a high amount of virtual storage. Because virtual storage
uses real storage as backup, real storage usage might also be high.
Therefore make sure that you do not underestimate the amount of virtual
storage that you allocate to running your application servers.
Before you begin
Determine your application server virtual storage requirements
based on the number of application servers you are running and the
number of requests that each of these servers handles.
About this task
Perform one or more of the following steps if you need to
improve client request throughput.
Procedure
- Allocate additional virtual storage.
The setting
of
REGION on the JCL for the proc controls the
amount of virtual storage available to a z/OS address
space. The default values for the WebSphere® Application Server controller and servant are set to zero, which
tells the operating system to allocate all the available region (close
to 2GB). You can limit the amount of virtual storage allocated by
setting the
REGION parameter to a value other than
zero. The size of the JVM heap is the most important factor when determining
the setting of the
REGION parameter. You should
only need to set the
REGION to something other
than zero when the JVM heap size is very large. The z/OS operating
system allocates user storage from the bottom of the address space,
which is where the JVM heap is allocated, and system storage from
the top. System abends can occur when the system tries to obtain
virtual storage and none is available. A non-zero
REGION parameter setting prevents this from occurring by preserving storage
at the top of the address space for system use. In almost all cases
running with the default
REGION will be satisfactory.
Note: For more information on REGION=0M and
IEFUSI, please see Installing your application serving environment section of the documentation.
- Convert application servers with high virtual storage usage
to run in 64-bit mode.
Running an application server in
64-bit mode allows you to specify larger JVM heap sizes.
- Convert deployment mangers, that are managing cells in
which very large applications are deployed, to run in 64-bit mode.
- Allocate additional real storage.
The total amount of real storage that your
system requires depends on the number of servers you are running and the size of the JVM heaps for
each server. You should allocate at least 512MB of real storage for a small configuration.
Recommendation: Sometimes in a heavy use environment, 2GB of central storage
is not enough to handle the real storage demands of a high volume Java™ application. In this
situation, you might want to configure your servers to run in 64-bit mode. Running your servers in
64-bit mode gives you the ability to dedicate more central storage to the LPAR, and the ability to
define more than 2GB of central storage. When you configure your servers to run in 64-bit mode, all
of the storage is defined as central storage.
The z/OS operating system running on a zSeries processor
always runs in 64-bit mode. If you are using a non-zSeries processors, or are running your servers
in 31-bit mode, you can minimize paging by defining more expanded storage.