To optimize performance, operating system and WebSphere® Application Server parameters
are automatically tuned in the IBM® WebSphere® Application Server
Hypervisor Edition virtual image.
Operating System Tuning
The
zLinux operating system included on your virtual images has been tuned
for increased performance. The following tuning parameters are automatically
set in the image and can be modified using virtuser only:
- timeout_timewait parameter
- Linux file descriptors
(ulimit)
- The Linux file descriptors
specify the number of open files that are supported. The default setting
is typically sufficient for most applications. If the value set for
this parameter is too low, a file open error, a memory allocation
failure, or a connection establishment error might be displayed. Check
the UNIX reference pages on
the ulimit command for the syntax of different
shells. To set the ulimit command to 8192 for the
Korn shell (ksh), issue the ulimit -n 8192 command.
Use the ulimit -a command to display the current
values for all limitations on the system resources.
- Recommended value: 8192 files
- Connection backlog
- TCP_KEEPALIVE_INTERVAL parameter
- TCP_KEEPALIVE_PROBES parameter
- sched_compat_yield parameter
WebSphere Application Server Tuning
WebSphere Hypervisor Edition
automatically tunes application servers and deployment managers based
on the virtual resources allocated to the virtual image. The automatic
tuning attempts to optimize your virtual system for performance, but
can be changed to meet the specific needs of your application. The Java heap size is based on the allocated
virtual memory. WebSphere Application
Server web container threads are sized based on the number of virtual
CPUs.
- Java Heap Size
The formula
used to calculate the Java heap
size is:
Minimum/Maximum JVM Heap = max(min((Virtual Memory - 1280MB) / # Application Server Instances, 4096MB), 256MB)
Based
on the amount of virtual memory allocated to a virtual image, the
intent is to distribute as much memory as possible to each application
server and deployment manager instance. After reserving 1280MB for
the OS and other native processes, the remaining memory is divided
evenly between each Java Virtual Machine (JVM). The automatic tuning
algorithm will assign no less than 256MB, and no more than 4GB for
a given JVM.
- WebSphere Application
Server Web Container Threads
The formula used to calculate the number
of web container threads is:
Minimum/Maximum Threads = # Virtual CPUs * 10
A
factor of 10 modifies the number of web container threads according
to the number of virtual processors in the virtual image. The purpose
is to provide additional worker threads to effectively utilize systems
with more virtual CPU resource.
Read-only mode
Read-only
mode is a feature of WebSphere Application
Server Hypervisor Edition that enables you to use less disk space.
- Benefits
- When read-only mode is set, virtual machines can share the disk
containing the operating system and the disk containing the WebSphere Application Server
binary. Sharing these disks creates a memory savings of 2 Mod 9 disks
per virtual machine.
- You can edit configurations and profiles.
- Limitations
- You cannot modify or install fix packs.
- You cannot apply maintenance.
Avoid trouble: Once a WebSphere Application Server
Hypervisor Edition for System z image is deployed in read-only mode,
the WebSphere Application Server home directory and SLES 11 Operating
System cannot be modified, which includes installing fix packs and
applying maintenance.
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