Analyzing and Tuning Memory Usage
Linux Windows AIX Solaris
Linux
To see if your system is short of physical memory, you can use /proc/meminfo
and vmstat:
# ps aux --sort pmem
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 1520 508 ? S 2005 1:27 init
....
db2inst1 1309 0.0 0.4 344308 33048 ? S 2005 1:55 db2agent (idle)
db2inst1 2919 0.0 0.4 345580 37368 ? S 2005 20:02 db2agent (idle)
db2inst1 24594 0.0 0.4 345068 36960 ? S 2005 15:45 db2agent (idle)
root 27645 0.0 14.4 1231288 1183976 ? S 2005 3:01 /opt/WebSphere/AppServer/java/bin/java
-Xboo tclasspath/p:/opt/WebSphere/AppServer/java/jre/lib/ext/ibmorb.jar:/opt/WebSphere/
AppServer/java/jre/lib/ext /ibmext.jar -Dwas.status.socket=56432 -classpath
/opt/WebSphere/AppServer/properties:/opt/WebSphere/AppSer
--sort option outputs the highest %MEM at bottom. Just note down the PID for the highest %MEM usage.
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Then use 'ps ev --pid=<PID>' to show the change over time (you had to
manually repeat it or put it as a cron to a file):
# ps ev --pid=27645
PID TTY STAT TIME MAJFL TRS DRS RSS %MEM COMMAND
27645 ? S 3:01 0 25 1231262 1183976 14.4 /opt/WebSphere/AppServer/java/bin/java -Xbootclasspath
# ps ev --pid=27645
PID TTY STAT TIME MAJFL TRS DRS RSS %MEM COMMAND
27645 ? S 3:01 0 25 1231262 1183976 14.4 /opt/WebSphere/AppServer/java/bin/java -Xbootclasspath
0
If RSS (resident set size, in KB) increases over time (so would %MEM), it may indicate a memory
leak in the application.
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WindowsFirst, are you
getting all the memory out of the system you paid for? Many SMP machines
not only come with mutiple CPUs (such as the IBM xSeries 330 and xSeries 366
with Intel® Xeon™),
but also come with large physical memory (8GB for example). But by
default, the Windows 2003 server operating system only "sees" 4GB. So make
sure do the following:
Click on the 'Advanced' tab in System Properties. Then click on the 'Startup and Recovery'
settings. Edit the default operation system settings to have '/PAE /3GB' options. Reboot
your system. This is why the two options are needed for performance:
/PAE
Native 32-bit Intel x86 architecture allows 4GB memory space
The Intel Physical Address Extension (PAE) is 36-bit memory addressing mode
Allows memory address above 4GB (up to 64GB)
Many SMP machines come with more than 4GB RAM
Set in boot.ini as “/PAE”
/3GB
By default, Windows reserves 2GB for OS kernel (privileged-mode)
Leaving only 2GB (out of 4GB 32-bit addressable) for user-mode applications
“/3GB” in boot.ini reallocates 3GB for user-mode applications
Good for database servers with many agents running
Tests show generally 1GB for kernel enough
With unnecessary Windows services disabled
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Windows Task
Manager can be used to monitor your system. You can start by
"Start->Run->(type) taskmgr and hit <Enter>"
Click on the 'Processes' tab then click on the 'Mem Usage' column to sort so that the
largest memory-consuming application shows at top. Identify the program's name and
debug further. Also, if Memory Usage keep increasing but not expectedly, your
application may have a memory leak. See "Code Tuning" for application performance
analysis.
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To automate and capture memory usage into a file using 'perfmon' tool that comes
with Windows 2003, see "perf automation" section from the left navigation.
AIX
First, use
'ps aux' to find out the program PID that you want to monitor memory usage.
Look in the %MEM column for the highest percentage:
# ps aux |more
USER PID %CPU %MEM SZ RSS TTY STAT STIME TIME COMMAND
root 57372 12.4 0.0 40 40 - A Nov 28 8633:34 wait
root 90280 0.1 0.0 492 500 - A Nov 28 55:12 /usr/sbin/syncd
root 1716352 0.0 8.0 1154040 1154072 - A Dec 02 3:47 /usr/WebSphere/
db2inst1 1143036 0.0 0.0 1044 460 - A Dec 02 2:11 db2disp 0
root 0 0.0 0.0 64 64 - A Nov 28 4:55 swapper
db2inst1 1458184 0.0 0.0 9608 9636 - A Dec 02 1:36 db2hmon 0
db2inst1 1409092 0.0 0.0 11960 6008 - A Dec 02 1:15 db2agent (idle)
root 311516 0.0 0.0 908 968 - A Nov 28 2:48 /usr/opt/db2_08
root 536650 0.0 1.0 204292 204324 - A Nov 29 2:15 /usr/WebSphere/
root 290960 0.0 0.0 468 492 - A Nov 28 2:18 /usr/sbin/getty
root 77862 0.0 0.0 116 116 - A Nov 28 1:41 gil
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then use 'svmon' to watch that PID's memory usage over a period of time
(through the intervals and iterations parameters). This tool not only can
display memory usage for a program over time, but also detects possible memory
leaks in kernel, a:
# svmon -P 1716352 -i 5 5 > ./mem.out
# grep -i "process" mem.out
[ Vsid Esid Type Description LPage Inuse Pin Pgsp Virtual ]
37e236 2 work process private s 48 3 0 48
37e236 2 work process private s 48 3 0 48
37e236 2 work process private s 48 3 0 48
37e236 2 work process private s 48 3 0 48
37e236 2 work process private s 48 3 0 48
The above command watches the WebSphere process for 5 iterations, 5 seconds each.
If the column showing '48' (Inuse) keeps increasing over time, it may indicate a memory leak
(means segment 'Esid' 2 is increasing). In this case, there is not leak. This technique can
be used with Java or C++ programs.
Column 'Esid' explanation:
Segment 0 (kernel) - a leak maybe in kernel itself, or device drivers.
Segment 2 (app) - user stack and data
Segment f (shared libs) - in standard libraries, etc.
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Other very useful 'svmon' examples: 'svmon -G' to display global memory usage; 'svmon
-P -t 1' to show the largest user (i.e., program) of memory:
# svmon -G
size inuse free pin virtual
memory 41943040 3757231 38185809 2220261 2906150
pg space 82182144 6155
work pers clnt
pin 2220261 0 0
in use 2906150 0 851081
# svmon -P -t 1 |more
-------------------------------------------------------------------------------
Pid Command Inuse Pin Pgsp Virtual 64-bit Mthrd 16MB
700600 java 268751844 268435502 0 268732920 N Y N
Vsid Esid Type Description PSize Inuse Pin Pgsp Virtual
0 0 work kernel (lgpg_vsid=0) L 65536 65536 0 65536
96c497 5 work working storage s 65536 0 0 65536
1f42bf5 4 work working storage s 65536 0 0 65536
1a5a1a4 3 work working storage s 65507 0 0 65507
1fd1fff 6 work working storage s 52588 0 0 52588
e30ee2 7 work working storage s 33183 0 0 33183
9d109d d work shared library text s 14610 0 0 14610
1bd03bc - clnt /dev/hd2:255351 s 1647 0 - -
...
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Solaris
'ps aux' can be used to determine %MEM used by programs:
# ps aux
to get a process-id for the highest memory-consuming application.
Processes have private memory to hold their stack space, heap, and data areas. The only
way to see how much memory a process is actively using is to use
/usr/proc/bin/pmap -x <process-id>
which is available in Solaris 2.6 and later releases.
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