Is this server using too much RAM or virtual memory ? (screen attached)

Question

I have a VPS with 512MB of ram 40GB storage 1CPU, I run a small domain parking service on it.

It is on CentOS, MySQL, Apache, etc.

Now my hosting provider claims that my server is putting too much load on their storage system and they had to reset my instance, and asks me to optimize the server because it is slowing down other clients on the storage.

The total domain's files (www folder) is under 100MB !

I am looking around and I cannot see what can cause this "storage abuse", they said it is the virtual memory that is written on their storage, few hundreds MB.

1. Isn't this use normal as shown in the webmin screen ?
2. Does it indicate any problem in the attached "top" command? (e.g the 772MB virtual memory of mysqld).

The only overload that I am aware of is a php script that runs once an hour to process all domain statistics, takes 3 minutes to complete and seems to put the CPU to work :)

Edit: I added a second screen of top command showing the missing data above the processes list.

Answer 1

This is just a guess, but it's too long for a comment, so here goes.

With virtual private servers, you get a "slice" of a real server. Rather than spending, say, $500 each on 24 small servers with 512MB ram etc, it's cheaper to buy (and operate) one $3500 server with 12GB RAM and two six-core hyperthreaded cpus.

Here's the trick: that server might sell more than 24 slices. This is fine, to a point: they don't expect everyone to use all their resources all the time. If you have enough of these, you can profile your clients and silently move customers to configurations where you're pretty sure they won't step on each other's toes — at least under normal circumstances. Again, this is normal practice and there's nothing wrong with it, as long as it's done carefully. There is a potential for abnormal workload to cause problems, but that's part of what makes this a cost-effective option; if you want a service where this isn't possible, you pay more for a service such as leased physical server in colo space.

Now for my guess. What happens when they oversubscribe a server too far? Someone gets left holding the short end of the stick, and only has virtual resources. Their "RAM" is actually entirely disk-backed, and must be swapped back and forth. Normally this is spread among all the machines, but in the right situations one of them can be left out in the cold. That's you. From their point of view your machine is doing weird things. It looks to them in their monitoring tools like you're the villain, when really you're the victim. A good provider would recognize this, but a good provider would also tell you before they reset your instance.

Answer 2

Take a look at the virt field in the output of your top command.Your VPS has 512MB of memory, yet apache is demanding far mare memory, which probably explains why you've got 4GB of virtual memory. With all those apache threads, virtual memory is going to be swapping constantly, which is causing the high IO.

Why is apache consuming so much memory? Check the apache logs first of all, and see if you can spot anything unusual going on. If you find anything, report back, including samples and maybe we can provide more specific help.

Could it be your PHP scripts to build stats aren't properly terminating, however I assume you've got your PHP maximum execution time set to something sensible to prevent your scripts going runaway?

Restart apache, and monitor memory usage, how long does it take before it start consuming lots and lots of swap space? Judging by your uptime of around 7 hours, not very long.

I don't know the details of your PHP site, but I'd imagine a simple domain parking site shouldn't be using too many resources. I've a VPS that we use in our company, it runs an internally developed app with a MySQL backend, which is fairly heavily utilised by around 30 staff each day, and it doesn't consume nearly as much memory as what your's is.

Judging by the load average, your CPU is being fairly heavily used, but that is likely just because of the swapping going on. Sort out the problem with Apache consuming so much memory and I'm sure things will start to look a lot better.

Also, change your host, they shouldn't be resetting your instance without warning. That's inexcusable.

Answer 3

Your httpd processes are using up more RAM than you physically have available, thus something has to get swapped. (It's also interesting that in the screenshot showing this, you cut off the top, and that you restarted Apache before taking the second screenshot. What are you hiding?) You need to reduce the system's memory usage dramatically, most likely by reducing the number of simultaneous httpd processes, or get more RAM.

That said, the host should be rate limiting this sort of thing already, which is not too difficult; perhaps they just don't know how? When you decide to get more RAM (you will), get a new host as well.