Website access is very slow and sometimes cannot be accessed. how can this problem be solved?

Website access is very slow. sometimes the website cannot be accessed. I don't know if it is a program problem or a configuration problem. this is the server memory usage suspicion. it may be related to this solution. & nbsp; totalusedfreesharedbuffersca website access is particularly slow, sometimes it cannot be accessed.
I don't know if it's a program problem or a configuration problem.
This is the server memory usage suspicion. it may be related to this. how can this problem be solved?
Total used free shared buffers cached
Mem: 4041 3957 84 0 193 3494
-/+ Buffers/cache: 269 3772
Swap: 5023 0 5023


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I used the sync command to clear the buffer and cached. you can try it.

However, when the memory is used up, it may also be because mysql is too large to be set, so every time I free about MB
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Use xhprof, xdebug, and other tools to see how the loads of the program are distributed .. then determine the solution.
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Make sure it is not a program problem, and then check the hardware.
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From the free-m provided by LZ, the memory usage of the machine is very normal... if sync is forced, it will be slower ....

Start with web service logs...
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Well, we recommend that you check apache logs. if the memory is not used for swap, you don't have to worry about memory usage.