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.
- 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.