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I have two servers. The first is an old laptop and the second is a VPS hosted by others. The laptop used to run MySQL fine when it was running CentOS 5.8, but since I "upgraded" it to CentOS 6.4, it is slow as a dog (nothing against dogs, of course). Maybe just coincidence and had nothing to do with CentOS 6.4, but the hardware just happened to break at the same time...?
I have two objectives on this post. First, I want to better understand the concepts behind how Linux deals with Memory. Second, I want to know if I should go off and buy a new laptop and trash the old laptop (note that the laptop is being used as a server and not a desktop/gui, and I just use a laptop because it is convenient).
Can anyone look over the below and comment on any critical items that we should all be aware of, as well as any values that looks way out of place? I've noticed that my slow laptop has swap memory (because I set it up with some even though I didn't know what swap memory is. I assume it is the ability to use the harddrive to store RAM), and the VPS has none. Sounds like the VPS should have some, but I have no idea.
I can see from the numbers that RAM is irrelevant to your performance issues, since you have a substantial amount of unused RAM on both systems. There is no performance difference between using, say, 30% of your RAM vs. 40% of your RAM. It's like a bucket; either the bucket is big enough to hold the water, or it isn't.
Probably the performance difference is due to 2 factors:
1. Your laptop is old and slow; your VPS is hosted on fast, modern hardware.
2. CentOS 6.x is approximately 3.5 years newer than 5.x so it has higher hardware requirements. Three and a half years might not seem like a long time, but it represents a quadrupling in computer power according to Moore's Law.
What makes you think it's a memory problem (at all) ?. And what makes you think we can offer a cogent opinion on replacing hardware based on such scant information ?.
Some random comments:
- your (laptop) memory is not under stress. The "Cached" and much of the "Buffers" could be reclaimed by Linux to add to the "Free" should it be needed. It isn't.
- swap is used as as "overflow" memory in need. You haven't needed it.
- the VPS model in use (presumably container based) is lying to you. All those zeroes are rubbish. I saw a thread on LKML a while back where the devs insisted users should never need to see the real numbers exported by the host image. I never followed up on what happened there.
- not all dogs are slow - I have trouble keeping up with mine while I am riding my pushbike.
Go here for the RHEL doco. Start with the release notes/tech notes for differences from your old release. Maybe Migration guide as well.
The deployment guide has some good info for where to look for relevant data in the system. The Performance tuning guide is likely to be less use than it might sound.