This topic describes how to tune the AIX operating system to optimize
the performance of your WebSphere Application Server. Because the AIX operating
system is not a WebSphere Application Server product, be aware that it can
change and results can vary.
Steps for this task (dependent on configuration)
- TCP_TIMEWAIT
- Description: Determines the time that must elapse before TCP/IP
can release a closed connection and reuse its resources. This interval between
closure and release is known as the TIME_WAIT state or twice the maximum segment
lifetime (2MSL) state. During this time, reopening the connection to the client
and server costs less than establishing a new connection. By reducing the
value of this entry, TCP/IP can release closed connections faster, providing
more resources for new connections. Adjust this parameter, if the running
application requires rapid release or the creation of new connections, or
if a low throughput occurs due to many connections sitting in the TIME_WAIT
state.
- How to view or set:
Issue the following command to set TCP_TIMEWAIT
state to 15 seconds:
/usr/sbin/no –o tcp_timewait =1
- AIX operating systems with DB2
- Description: Separating your DB2 log files from the physical database
files can boost performance. You can also separate the log and the database
files from the drive that contains the Journaled File System (JFS) service.
AIX uses specific volume groups and file systems for the JFS logging.
- How to view or set: Use the AIX filemon utility to view all the
file system input and output and to strategically select the file system for
the DB2 log files. Set the DB2 log location according to the DB2 tuning parameters topic.
- Default value: The default location for the DB2 log files is often
the same disk drive where the database tables are stored.
- Recommended value: Move the files to a disk that is separate from
the DB2 data and has the minimum input or output activity.
- AIX file descriptors (ulimit)
- Description: Specifies the number of open files that are permitted.
The default setting is typically sufficient for most applications. If the
value set for this parameter is too low, errors might occur when opening files
or establishing connections. A Memory allocation error might be displayed.
To prevent WebSphere Application Server from running short on resources, remove
the upper limits (ulimit) for resources on the user account that the WebSphere
Application Server process runs on.
- How to view or set: Perform the following steps to change the ulimit
settings:
- Open the command window.
- Type smitty users to open the AIX configuration program.
- Select Change or Show Characteristics of a user.
- Type the name of the user account that WebSphere Application Server runs
on.
- Press Enter.
- Change the following settings to the indicated value:
Soft FILE Size -1
Soft CPU Time -1
Soft STACK Size -1
Soft CORE File Size -1
Hard FILE Size -1
Hard CPU Time -1
Hard STACK Size -1
Hard CORE File Size -1
- Press Enter to save changes.
- Log out and log in your account.
- Restart WebSphere Application Server.
- Default value: For the AIX operating system, the default setting
is 2000.
- Recommended value: Unlimited
- AIX TCP_KEEPIDLE
- Description: The keepAlive packet ensures that a connection stays
in an active/ESTABLISHED state.
- How to view or set: Use the no command to determine the
current value or to set the value. The change is effective until the next
time you restart the machine. To permanently change the value, add the no command
to the /etc/rc.net directory. For example:
no -o tcp_keepidle=600
- Default value: 14400 milliseconds.
- Recommended value: 600 milliseconds.
- TCP_KEEPINTVL
- Description: Specifies the interval between packets that are sent
to validate the connection.
- How to view or set: Use the following command to set the value
to 5 seconds:
no -o tcp_keepintvl=5
- Default value: 150(1/2 seconds)
- Recommended value: 5 seconds
- TCP_KEEPINIT
- Description: Specifies the initial timeout value for TCP connection.
- How to view or set: Use the following command to set the value
to 20 seconds:
no -o tcp_keepinit=20
- Default value: 150(1/2 seconds)
- Recommended value: 20 seconds
- Allocating large pages for Java virtual machines heap
Some applications require a very large heap for optimal performance.
Reduce the CPU overhead of managing a large heap by using large page support
that is provided by the CPU and the operating system. The following steps
allocate 4GB of RAM as large pages:
- As root user, run the following commands to reserve 4GB of large page:
vmo -r -o lgpg_regions=256 -o lgpg_size=16777216
bosboot -ad /dev/ipldevice
reboot -q
- After reboot, run the following command to enable large page support on
the AIX operating system:
vmo -p -o v_pinshm=1
- As root user, add the following capabilities for the user:
chuser capabilities=CAP_BYPASS_RAC_VMM,CAP_PROPAGATE $USER
- Add the -Xlp Java options to the Java command.
- Validate large page support is used with the following command:
vmstat -l 1
Note: The
"alp" column is non-zero when the application is running.
- Other AIX information
Consider the other AIX operating system settings that are not within
the scope of this document. You can adjust the following additional settings:
- Adapter transmit and receive queue
- TCP/IP socket buffer
- IP protocol mbuf pool performance
- Update file descriptors
- Update the scheduler
For more information about AIX operating systems, see
Performance: Resources for learning.
Result
This tuning procedure improves performance of WebSphere Application
Server on the AIX operating system.
What to do next
After tuning your operating system for performance, consult other
tuning topics for various tuning tips.