Tuning AIX systemsx - Sarbjit Singh Gill

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26 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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Tuning AIX systems

This topic describes how to tune the AIX operating system to optimize the performance of your WebSphere Application Server.

About this task

There are a number of configuration changes and variables you can set to tune the performance of Websphere to suit your
needs. Because the AIX operating system is not a WebSphere Application Server product, be aware that it can change and
results can vary.

Procedure

Change the following configuration settings or variables according to your needs:



TCP_TIMEWAIT


o

Description:

Determines the time that must elapse before TCP/IP can release a closed connection and reuse
its resources. This interval between clos
ure 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 sitti
ng in the TIME_WAIT state.

o

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


o

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 syste
ms for the JFS logging.

o

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.

o

Default value:
The default location for the DB2 log files is often the same disk drive

where the database tables
are stored.

o

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)


o

Description:

Specifies the various restrictions on resource

usage on the user account. The ulimit
-
a command
displays all the ulimit limits. The ulimit
-
a command specifies only the number of open files that are permitted.
The default number of open files setting (2000) is typically sufficient for most application
s. If the value set for
this parameter is too low, errors might occur when opening files or establishing connections. Because this
value limits the number of file descriptors that a server process might open, a value that is too low prevents
optimum perfor
mance.

o

How to view or set:

Perform the following steps to change the open file limit to 10,000 files:

1.

Open the command window.

2.

Edit the
/etc/security/limits

file. Add the following lines to the user account that the
WebSphere Application Server process
runs on:

3.

nofiles = 10000

nofiles_hard = 10000

4.

Save the changes.

5.

Restart your AIX system.

6.

To verify the result, type the ulimit
-
a command on the command line. For example, type # ulimit
-
a.

o

Default value:

For the AIX operating system, the default setting is
2000
.

o

Recommended value:

The value is application dependent and applies exclusively to application program data
and the application stack.

Increasing the ulimit file descriptor limits might improve pe
rformance. Increasing some of the other limits might
be needed depending on your application. Any changes to the data or stack ulimits should ensure that
data+stack < 256MB (for 32
-
bit WebSphere Application Server only).

It is recommended that you change t
he ulimit for data to "unlimited".



AIX TCP_KEEPIDLE

o

Description:

The keepAlive packet ensures that a connection stays in an active/ESTABLISHED state.

o

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

o

Default value:

14400

half seconds (2 hours).

o

Recommended value:

600

half second
s (5 minutes).



TCP_KEEPINTVL


o

Description:

Specifies the interval between packets that are sent to validate the connection.

o

How to view or set:

Use the following command to set the value to
5

seconds:

no
-
o tcp_keepintvl=10

o

Default value:

150(1/2
seconds)


o

Recommended value:

10(1/2 seconds)




TCP_KEEPINIT


o

Description:

Specifies the initial timeout value for TCP connection.

o

How to view or set:

Use the following command to set the value to
20

seconds:

no
-
o tcp_keepinit=40

o

Default value:

150(1/2 se
conds)


o

Recommended value:

40(1/2 seconds)




Allocating large pages (16 MB) 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 tha
t is provided by the CPU and the operating system. The following steps allocate 4
GB of RAM as large pages (16 MB):

1.

As root user, run the following commands to reserve 4 GB of large page:

2.

vmo
-
r
-
o lgpg_regions=256
-
o lgpg_size=16777216

3.

bosboot

-
ad /dev/ipldevice

reboot
-
q

4.

After reboot, run the following command to enable large page support on the AIX operating system:

vmo
-
p
-
o v_pinshm=1

5.

As root user, add the following capabilities for the user:

chuser capabilities=CAP_BYPASS_RAC_V
MM,CAP_PROPAGATE $USER

6.

Add the
-
Xlp

Java options to the Java command.

a.

Click
Servers

>
Application Servers

>
server_name
.

b.

Under
Server Infrastructure
, click
Java and Process Management

>
Process Definition

>
Java
Virtual Machine
.

c.

In the
Generic JVM
Argument

field, add
-
Xlp
.

7.

Add the
EXTSHM

custom property and set to
OFF
.


.

Click
Servers

>
Application Servers

>
server_name
.

a.

Under
Server Infrastructure
, click
Java and Process Management

>
Process Definition

>
Environment Entries

>
New
.

b.

In the
Name

field, enter
EXTSHM
.

c.

In the
Value

field, enter
OFF
.

8.

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.

There are several concerns when enabling large pages,
which can cause serious events to occur on the machine when
large pages are enabled. For more information on AIX large pages, see the "Considerations for using large pages"
section at the following address:
http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.prftungd/doc/prftungd/large_page_ov
w.htm
.

If you do not want to use the large pages option, there is also a medium page option. The medium page size option,
which is similar, and has close to the same performance gains as large pages. However, it does not involve the
problems of reserving physical

memory for a specific user or process. For more information, see the
-
Xlp64k option in
the
Tuning Java virtual machines

topic.



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:

o

Adapter transmit and receive queue

o

TCP/IP socket buffer

o

IP protocol mbuf

pool performance

o

Update file descriptors

o

Update the scheduler

For more information about AIX operating systems, see
Performance: Resources for learning
.

Results

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 the other tuning to
pics for various tuning tips.


http://publib.boulder.ibm.com/infocenter/wasinfo/v6r0/index.jsp?topic=/
com.ibm.websphere.express.doc/info/exp/ae
/rprf_db2parameters.html