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I currently have a web application running on a vps server running Ubuntu 9.04 Jaunty. I recently had installed Nagios as monitoring tool. I had configured an extra plugin in order to check the free available memory. One of the servers has only approximadettly 7% of free memory.

Is that a reasonable value?

Thanks in advance for the help, Best regards!

Rui Gonçalves
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2 Answers2

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It depends how that figure is calculated.

Some tools include buffers and cache in the free memory figure, some don't. I/O caching has a huge impact on webserver performance. If you've got shell access, try running 'free' to see what the actual values are, e.g. from a system with virtually no load on it:

             total       used       free     shared    buffers     cached
Mem:       4135700     504028    3631672          0      52240     262880
-/+ buffers/cache:     188908    3946792
Swap:      4192944        156    4192788

Here I've actually got (4135700 - 188908) = 3946792 free

While you can never have too much memory, if you've got less than 50% available for buffers and cache and the total size of the content in the website is more than this amount then your website will slow down.

Kyle Brandt
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symcbean
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That's a bit high, actually. Linux uses unused memory for buffers and cache, releasing it to applications as needed, so free memory is wasted memory.

Ignacio Vazquez-Abrams
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