Memory utilization

Ammad · 03-29-2011, 07:17 AM

Hello,

I have two server running oracle EBS, there is some changes either in application or OS level.
The problem is from past two days one of the server is not utilizing memory as cache, as you knows that linux by default cache process in memory.

whereas the DB server is using cache memory.

Code:

DB Server
# free -m
             total       used       free     shared    buffers     cached
Mem:         31871      31840         30          0        124      26223
-/+ buffers/cache:       5493      26378
Swap:        10239        117      10122




Oracle Application Server
             total       used       free     shared    buffers     cached
Mem:         31871       8278      23592          0        523       2570
-/+ buffers/cache:       5185      26685
Swap:        10239          0      10239

Two days before the Application server was using memory, and there was no free memory, but right now its most of memory is free.

Any idea to verify the settings on OS level

paulsm4 · 03-29-2011, 11:56 PM

Your DB Server is sad: both because you have relatively little free memory at the moment, and because you've exceeded RAM and used swap recently.

Your Application server is much happier: it has plenty of free memory at the moment, and it's never hit swap.

If this is typical for your system, you definitely want to consider getting more RAM for your DB Server. Perhaps even moving it to a 64-bit CPU, if you haven't already.

"Cached" memory is more or less irrelevant here. The DB Server happens to have 10 times more cache than your Application server at the moment - but Linux will automatically de-allocate the cache if it needs more RAM (which, based on your statistics, it probably will).

Moral: you don't want to tune system parameters. You want to purchase more RAM!

syg00 · 03-30-2011, 02:09 AM

Can't agree with that.
The DB server is almost all cache - as designed. Probably including Oracle SGA. Small swap usage is irrelevant unless active - Linux will "park" long term unused pages in swap intermittently.

The change in the App server is probably application related - AFAIK you have no control over cache allocation (other than swapiness). Check your Oracle definitions - maybe local updates have been lost.

paulsm4 · 03-30-2011, 10:15 AM

syg00 -

Quote:

The DB server is almost all cache - as designed. Probably including Oracle SGA

Absolutely correct

Quote:

AFAIK you have no control over cache allocation

Also correct

Quote:

"Cached" memory is more or less irrelevant here...
Moral: you don't want to tune system parameters.

This is my main point. If it's a choice between twiddling with "magic system parameters" and buying more RAM - the answer is "get more RAM". In fact, the answer is even "upgrade your CPU to 64 bit, if you have to!"

Quote:

Check your Oracle definitions

Also excellent advice