Confusing CPU load in apache server-status

apache-2.2

apache server-status ( mod_status ) shows very low CPU usage even though I'm seeing more than 90% in top output.

Shown in server-status page:

CPU Usage: u92.17 s14.87 cu0 cs0 - .0178% CPU load

From top output:

1187 apache    20   0  439m 204m 6000 S 23.2  6.8   0:24.52 /usr/sbin/httpd

Why does this happens ? Cant we use the server-status page to check the apache CPU usage ?

( top output shown is not full, as it has lot of http process running and has many CPU … Even though it crosses a cumulative of 300% it still shows 0.224% in server-status page ! )

Kindly note It is not the same as like this confusing result on Apache server status results

Best Answer

Two things which may help you understand what you're seeing:

The 0.0178% load from server-status is the average CPU load since Apache was started. It simply won't pick up spikes in CPU usage like what you seem to be seeing in top. From your numbers I would guess Apache was started roughly 7 days ago ( (92.17+14.87)/0.0178*100/86400=6.96).
There will likely be multiple "http" processes listed in top, at least in prefork mode (unsure about worker mode). One of these will be the "parent" process and the rest are all its children serving requests as needed. Some children may have more CPU/memory usage than others.

The CPU usage from server-status is useful as an average guide to how much CPU Apache is using but mostly useless for recognizing load spikes of which top is much more useful.

Related Solutions

Linux – Random high CPU usage on Linux using Apache

The CPU usage from Apache's server-status page is the average usage since Apache was started so it won't show spikes like this. When you get these load spikes you can check the server-status page to see what pages/clients are being server (ExtendedStatus must be on).

You can also use netstat to see what clients are currently accessing your machine:

 netstat -an | grep ESTABLISHED

If you run this over multiple hours and traffic spikes you may be able to spot a reoccuring IP address and potentially trace to a specific robot/crawler. If this does turn out to be the case you can look into using robots.txt to limit how well behaving robots should crawl your site.

Edit: On a busy server the above netstat command should show some entries like:

tcp        0      0 10.2.212.13:80              216.146.52.21:24979         ESTABLISHED
tcp        0      0 10.2.212.13:80              86.174.113.138:54901        ESTABLISHED
tcp        0      0 10.2.212.13:80              94.1.216.253:51204          ESTABLISHED
tcp        0      0 10.2.212.13:80              24.9.61.204:62936           ESTABLISHED

The client's IP address will be the one on the right. If you only see 1 or 2 lines it just means that at that moment there is just your ssh connection. Check again when your load increases. You can also remove the grep to list all connections although this will include a large number of old TIME_WAIT.

I would start with the extended server-status and see if that can reveal any obvious crawlers during traffic peaks.

Optimizing apache server load

You are barking up the wrong tree. Seemingly it's Apache consuming the CPU; in reality there's mod_php which has to serve your Magento pages.

And the latter is your answer: Magento sure is a heavy beast. Don't try to optimize Apache at this point, concentrate on your Magento setup. Do not disappoint if you don't succeed. Many have tried that in Server Fault, not many have succeeded (from what I have seen). A heavy piece of software is a heavy piece of software.

Best Answer

Related Solutions

Linux – Random high CPU usage on Linux using Apache

Optimizing apache server load

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