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I have a website which has a traffic of ~100k visitors a day. We are running on WordPress, and have 3 app servers with RackSpace. There are days when the servers can support ~1200 live visitors without slowing down, and on some days, the RAM usage peaks with just ~500 users and the servers crash. I have basic knowledge of system admin. How do I find out what is consuming all the RAM? I think it's a WordPress issue, rather than an Apache issue.

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closed as off-topic by Jenny D, Ward, MadHatter, dawud, Dave M Sep 12 '13 at 17:11

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2 Answers

If you look at /var/log/apache2/error.log you will see if apache is working right, or crashing.

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This gives me all the php errors. I am using W3TC plugin, so most of the errors I get are - apc_store() unable to allocate memory to pool My system admin guy tells me that PHP isn't able to free up memory. I am trying to understand how to track which process / function / file is taking up the memory. Also, the memory bottleneck is intermittent. It runs fine most of the time. Would apache-status be able to help? Is it possible to log the apache-status file? –  Nish Sep 11 '13 at 8:43
    
Take a look at this. Maybe helps: linuxatemyram.com –  Manolo Salsas Sep 11 '13 at 9:02
    
Yeah, I know about that. There is sufficient buffer during normal usage. And then the CPU and memory usage suddenly starts peaking. This happened for some 20 - 30 mins today, and I wasn't around, so I don't really know what happened. –  Nish Sep 11 '13 at 9:26
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How to debug an apache crash?

Did it crash? If so then you should have a core dump - generate a stack trace from it. (I suspect it dodn't really crash).

has a traffic of ~100k visitors a day

Good metric for marketing - useless for systems admin.

have 3 app servers with RackSpace....peaks with just ~500 users and the servers crash

All three servers "crash" simultaeneously? Highly improbable.

apc_store() unable to allocate memory to pool

What is the memory usage on the OS? What is the memory usage in APC?

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