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Low memory usage on VPS Ubuntu

I have VPS server with installed Ubuntu on it. Total RAM 16GB, but my server use only 3-4GB ... The question is why ? I set innoDB to use 12GB but nothing change. Server load 1.5

How can I increase usage of memory ? When I had dedicated server ubuntu always use all memory to cache things and speed up processes.

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    • Exactly what problem are you having? Is the server slow? What is the size of your database? Can you post your "top" stats?
    • Linux and/or MySQL will not proactively cache things, but rather will cache items as they're accessed. Have you had sufficient usage to access more than 3-4GB of data?
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    • If sever load is bigger then 1.5 then I think - yes ... ubuntu should use more memory. Maybe I should use mem-cache if I got so much free RAM ?
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    • load avarge - 1.5, memory used 3G , free memory 13GB. Sometimes server start using swap even that there is more then 10GB of RAM.

A load average of 1.5 is not an issue if you have more than one CPU allocated to the VPS. If there is only one CPU allocated, then you are bottlenecking somewhere. The 'sar' tool is good for identifying the bottleneck.

It may take time to fill the caches. It seems you have a reasonably memory efficient load. Give the system some time, and memory usage should increase. If it does not increase, then you may be hitting kernel tuning limits. Allocating more memory than is required will have diminishing returns.

Unless you have a very large database for which all data is actively accessed allocating more memory to the database will not increase memory usage. Maximum memory usages should be not much more that the space used by the database's data files.

Allocating and using excessive memory for a virtual server may cause issues for other servers running on the same host. There is a limit after which all virtual servers will begin swapping leading to a significant decrease in performance. (I have seen Java Full GC times go from seconds to hours.)

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