RE: memory usage
- From: Kenan "�zt�rk" <mynameiskenan@xxxxxxxxx>
- To: ora-apps-dba@xxxxxxxxxxxxx
- Date: Sun, 20 May 2007 13:02:01 -0700 (PDT)
Vasu,
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.
Regards,
Kenan
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
vasu
-----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!
Regards,
Kenan
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