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The server has physical memory of 4gb. We have a desktop CentOS (5.) running a VM (virtualbox) as the server.

The VM is allowed 1.8gb memory (as per VirtualBox recommendation).

My problem is that Apache starts taking up most of the memory, until it starts to get tight, at which point the server becomes really sluggish. The only 'fix' I found is to do service httpd restart.

Any ideas why this is happening? How/should I look where this memory is being used?

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What makes you think apache is taking up the memory? –  David Schwartz Feb 17 '12 at 10:05
Because when I restart apache, the server gets super-responsive. I'm also able to see apache allocate memory per request, but not lower it down afterwords. –  Christian Feb 17 '12 at 10:06
Not lower what down afterwards? And what do you mean by "until it starts to get tight"? –  David Schwartz Feb 17 '12 at 10:07
1) Memory is not deallocated. 2) not much free memory left. –  Christian Feb 17 '12 at 10:14
Both of those things are normal and have nothing to do with your issue. Most applications don't return virtual memory to the operating system because virtual memory is not normally considered a scarce resource. And most systems have very little free memory because free memory is useless -- only memory that's being used can improve performance. Whatever your problem is, you're focused on normal things that likely have nothing to do with it and that's probably keeping you from seeing the big picture. –  David Schwartz Feb 17 '12 at 10:16

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