topic Re: ideal memory usage in Operating System - HP-UX

ideal memory usage

QASCO — Tue, 06 Feb 2007 13:51:33 GMT

Hello All,

could anybody tell me, what is the ideal memory usage? is it 75% or %85 or is there an ideal situation that i should keep up with.

Any help is highly appreciated.

TIA,

Re: ideal memory usage

Pete Randall — Tue, 06 Feb 2007 13:57:05 GMT

Ideal in what way? Getting the most for you money? The obvious answer would be 100% utilization. Having the maximum growth potential? Then the answer would be 0%. The answer could range anywhere between those two extremems depending on your situation and goals.

Pete

Re: ideal memory usage

James R. Ferguson — Tue, 06 Feb 2007 13:59:33 GMT

Hi:

There is no set value other than that you (your processes) have all that you (they) need or want such that you never page(out) to swap.

Some thinking also adds that if you aren't using (for example) 75% of any resource, then you didn't need it and are wasting it.

Regards!

...JRF...

Re: ideal memory usage

QASCO — Tue, 06 Feb 2007 14:05:26 GMT

Hi,

I mean't from a performance point of view (best practices)like if i have 24x7 systems.

Regards,

Re: ideal memory usage

James R. Ferguson — Tue, 06 Feb 2007 14:15:07 GMT

Hi (again):

> I mean't from a performance point of view (best practices)like if i have 24x7 systems.

My answer (certainly the first part about not paging) stands.

Too, if you have memory to spare, that is not being used, why not look to optimizing your applications? For instance, maybe you could provide your database with more shared memory segments; or maybe a file manipulation utility could have its I/O greately reduced if its processing were done in memory arrays.

Regards!

...JRF...

Re: ideal memory usage

A. Clay Stephenson — Tue, 06 Feb 2007 15:00:24 GMT

From a performance perspective, as long are you aren't paging out, very near 100% is fine although you would be on the hairy edge. Moreover, 90% utilization on a system with 512KiB is vastly different than 90% utilization on a system with 64GiB. The "ideal" amount is as much as you need and that is about as precise as it gets. The goal for the majority of modern systems is to have enough memory so that page-outs never occur (or at worst occur very rarely and always at low rates). As long as you meet that criterion, nothing else really matters. As has been suggested, if you do have significant headroom then use it to better tune applications (e.g. increase a database cache) or increase the system buffer cache --- within reasonable limits.

In any event, this isn't a "set it and forget it" resource. It requires perodic checking or better yet constant checking through a monitoring system so that you add memory or tune applications before the problems actually occur.

Re: ideal memory usage

Tim Nelson — Tue, 06 Feb 2007 16:03:24 GMT

Having more than 1GB of available memory available for misc new processes is what works in my environment. ( we ride between 1-2GB free memory. percentages are misleading.

Most important: never swap, if you are on the edge you most likely will swap. Give yourself a buffer that works in your environment. Having excess is great but a waste of $$.

Notice the different answers you are getting ? It all depends on how tight or loose your environment is and what the applications use and require. Make the decision based on current workloads and trends. Increase as workloads increase.

Re: ideal memory usage

Geoff Wild — Tue, 06 Feb 2007 16:18:16 GMT

We push ours to the limit for Oracle - as DBA's increase SGA to use as much of the ram as we can. So, on our DB servers, we run 99% to 100%...

Though I just checked our main SAP DB/CI server and it is at:

# memdetail
Memory Stat total used avail %used
physical 16128.0 14289.8 1838.2 89%
active virtual 16729.2 7252.4 9476.8 43%
active real 11129.5 4529.7 6599.8 41%
memory swap 12647.8 2407.3 10240.5 19%
device swap 26528.0 15921.1 10606.9 60%

Rgds...Geoff

Re: ideal memory usage

George Liu_4 — Tue, 06 Feb 2007 16:25:26 GMT

as far as it does't swap, high percent is the best