What is a reasonable ratio between CPU and Memory Usage

[albert_hua]

Hi, every one:
I have a question to bother you.
Recently I made a performance report of one primary server of our system and I found the average CPU usage is relatively low (10~20) while the average Memory usage is relatively high (60~70).
So do you think such a ratio is reasonable or not. I think when I increase the users of this server, the memory will become the bottleneck first. So why do HP Consultant select to configure so many CPUs to use for our system? Is it unreasonable or not? What is the main consideration.
Thanks a lot.


Al.

[albert_hua]

Forgive me.
I am so fool to send the same message twice. Please delete one for me.
Thanks.

[Sean OB_1]

I don't think there is any reasonable ratio between memory and CPU usage. This is completely dependant on the type of applications running on your system.

For example you can start up an Oracle database and use quite a bit of memory, yet have little CPU usage if no one is accessing the database.

[albert_hua]

Yes, you are quite right.
I want to get some hints about this aspect.
I have no experience about different kinds of applications at all. So could anyone be kindly to introduce me some real applications in which CPU usage will be very high?

[Shannon Petry]

You can not make a ration work, no matter what your doing. Different applications use both memory and CPU differently all the time.

Example:
FEA(Finite element analasys calculates stress on a model. If I take a simple plate and put stress in the center, and a bicycle wheel with stress in the center, both will be quite different in both memory and CPU use.
Now lets take two pieces of complex geometry and try tocompare. Bicycle whell and Car wheel. Both are complex, but because surfaces take alot more space in memory, the car wheel will take more memory, but in essense both will take the same amount of CPU to calculate failures from stress.

Now, lets move our analagy to databases instead of FEA. Customer A only uses 1 huge table, customer 2 has 4 tables, but all smaller. A query will take much more time from the large table, and more CPU. However 4 indexes will most likely take more memory than 1.

In both cases, there is no wrong or right answer to anything. Simply a matter of what the needs and requirements are.

Regards,
Shannon

[Hai Nguyen_1]

Albert,

In my opinion, there is no existence of such ratio. A multi-cpu computer is preferred if you have an application which performs lots of parallel computing, for example. Whereas, lots of memory will speed up I/0 in general.

Hai

[Ken Hubnik_2]

CPU should be monitored by load average and memory should be monitored by if the system is paging excessively or you are having page deactivations. There is no good ratio between the 2.

[albert_hua]

But if I found that on my server, the CPU usage is always keeping low, is that mean the current CPU resource is extravagant to our application?

[Rory R Hammond]

I see no real real relationship between memory and cpu. As guide, you should have enough memory so that your system doesn't swap to disk. If you do swap, cpu and disk usage could be quite high. Swaping memory and cpu usage then would have a unwanted relationship and should be avoided.

You should have enough CPU resources to manage your PEAK loads in a reasonable amount of time. Time of day is important. Some processes can dominate a CPU. having an additional cpu could help throughput for other system jobs. One cpu might show 100% busy and the other 10% busy, making your system 55% busy, which could be reasonable loading. If your server's CPU is consistently 20% busy and you have no peak performance requirements your system might have to much CPU capacity. You shouldn't just focus on this one fact, you need to look at the total requirements. I have bought "big boxes" because I expected future growth and the PRICE POINT was superior to a "lesser box"

Ror