RE: memory usage

  • From: Kenan "Öztürk" <mynameiskenan@xxxxxxxxx>
  • To: ora-apps-dba@xxxxxxxxxxxxx
  • Date: Sun, 20 May 2007 13:02:01 -0700 (PDT)


thanks for the helpful info.
according to your reply, i googled for "cached" part of the top command. Here 
is a good explaination for memory usage:

Overview of memory management Traditional Unix tools like 'top' often report a 
surprisingly small amount of free memory after a system has been running for a 
while. For instance, after about 3 hours of uptime, the machine I'm writing 
this on reports under 60 MB of free memory, even though I have 512 MB of RAM on 
the system. Where does it all go? 
The biggest place it's being used is in the disk cache, which is currently over 
290 MB. This is reported by top as "cached". Cached memory is essentially free, 
in that it can be replaced quickly if a running (or newly starting) program 
needs the memory. 
The reason Linux uses so much memory for disk cache is because the RAM is 
wasted if it isn't used. Keeping the cache means that if something needs the 
same data again, there's a good chance it will still be in the cache in memory. 
Fetching the information from there is around 1,000 times quicker than getting 
it from the hard disk. If it's not found in the cache, the hard disk needs to 
be read anyway, but in that case nothing has been lost in time. 
To see a better estimation of how much memory is really free for applications 
to use, run the command free -m: 

The -/+ buffers/cache line shows how much memory is used and free from the 
perspective of the applications. Generally speaking, if little swap is being 
used, memory usage isn't impacting performance at all.


Vasu Balla <appsdba@xxxxxxxxx> wrote:   Message    in  linux, file system also 
maintains its cache, which gives us a feeling that whole  memory getting filled 
up. infact when some other program requests for memory,  the memory occupied by 
filesystem is automatically freed up and given to that  process. 
 top - 12:39:21 up 3 days, 20:23, 23  users,  load average: 0.78, 1.04, 1.00
Tasks: 266 total,   5  running, 261 sleeping,   0 stopped,   0 zombie
Cpu(s):  75.5%us,  5.6%sy,  0.0%ni, 16.6%id,  2.3%wa,  0.0%hi,   0.0%si,  0.0%st
Mem:   1035676k total,   995916k  used,    39760k free,    85536k  buffers
Swap:  2096472k total,      144k  used,  2096328k free,   416648k  cached

 there are some kernel parameters which control the amt of memory  that always 
needs to be kept free. can't get that param name from top of my  head. you can 
google for it
   -----Original Message-----
From:    ora-apps-dba-bounce@xxxxxxxxxxxxx 
[mailto:ora-apps-dba-bounce@xxxxxxxxxxxxx]    On Behalf Of Kenan Öztürk
Sent: Friday, May 18, 2007 7:39    PM
To: ora-apps-dba@xxxxxxxxxxxxx
Subject: memory    usage

Hi all,

on RedHat A.S 3.0/4.0 I observer that    free memory amount is really low. I 
know that if it is swapping then there's a    problem otherwise it is normal. 
bu where this ram going?

After    rebooting system and starting ebs services, i observe that ram usage 
is    increasing and only 10-50 mb free memory     remains!


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