Performance issues

Can some one share some experience on how to take a look at the performance issue on linux servers. normally people come to me and say i have performance issue in certain linux server, how do i start looking into the performance measure on linux servers

I am using redhat 5/6
ittechlabLinux SupportAsked:
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Pepe2323Connect With a Mentor Commented:
That means


%user

    Lists the percentage of time that the processor is in user mode
    ( Process started by a user like Database, appservers and more )

%nice:
Percentage of CPU utilization that occurred while executing at the user level with nice priority.

%system

    Lists the percentage of time that the processor is in system mode ( means running by kernel)

%iowait

    Lists the percentage of time that the processor is idle and waiting for I/O completion
   CPU spends waiting for I/O with no processes to run -- usually related with disk slowness

%steal
Percentage of time spent in involuntary wait by the virtual CPU or CPUs while the hypervisor was servicing another virtual processor.
(steal time is a metric that only has meaning in a virtualized computing environment. It represents the amount of CPU that is taken away from a virtual machine to serve other purposes.)

%idle

    Lists the percentage of time that the processor is idle and not waiting for I/O
    (Means you cpu is free)
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joolsCommented:
This is best measured over a period of time so that you have some sort of baseline to go on.

I use atop as it has good logging and playback facilities, you can use vmstat/iostat and sar for the overview performance type stuff but atop give a more granular view of the system.

If you already have it running you can check the logs and run thru the performance, on a busy server this will indicate some busy and quiet periods, there may be a way to produce some graphical views, if you have a large setup you can use nagios/zenoss to monitor system performance and produce pretty graphs for manager types :-)
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Pepe2323Connect With a Mentor Commented:
well you can use top to check what is going on into the server.

Other option is use sar, sar has several option depends what you want to get.

sar -u --> is for cpu, to get a more accurate information i used to run like this sar -u 50 ( means i till take 50 samples of the cpu and then will show me the cpu status)
sar -r .. > is for memoery

sar also can be helpful if  the problem has passed but you want to check at what time did happen.

 sar -f /var/log/sysstat/sa04 -- using the log collected by the crontab

for more information how to enable sar to collect logs of the server performance check this link:

http://bencane.com/2012/07/sar-sysstat-linux-performance-statistics-with-ease/

finally you can list the top 10 process are using more resources.

ps -eo pcpu,pid,user,args | sort -k 1 -r | head -10 --> this top ten is based on cpu

for memory

ps -eo pid,ppid,rss,vsize,pcpu,pmem,cmd -ww --sort=pid

Regards.
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ittechlabLinux SupportAuthor Commented:
I am not allowed to install atop in my environment.
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ittechlabLinux SupportAuthor Commented:
sar -u 50
Linux 2.6.18-274.12.1.el5 (ulmdrpp1)    05/15/2013

09:39:54 AM       CPU     %user     %nice   %system   %iowait    %steal     %idle
09:40:44 AM       all      0.11      0.00      0.12      1.56      0.00     98.21
Average:          all      0.11      0.00      0.12      1.56      0.00     98.21

I ran sar -u 50, can you explain what is these numbers mean in details. Thanks
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joolsConnect With a Mentor Commented:
is sar et al are your only options then use this as a reference (saves wasting time)

http://www.thegeekstuff.com/2011/03/sar-examples/


You need to collect the data still.
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