The whole thing comes as a consequence of using buffered I/O. New linux
kernels (2.4.18 and later) have new memory management, which allows
the kernel to grab more memory for buffers in periods of intense I./O
activity. If you have a very active database on ReiserFS or Ext3, Linux is
going to try to help you out by allocating more memory for the file system
buffers, even by stealing pages from the active processes, which will, in
turn. start paging. The only possible response is to eliminate the buffered I/
O and switch to non-buffered I/O. That is not so hard to do.
On 2003.11.01 09:44, Tanel Poder wrote:
> Just for clarification, do you actually see swapping when starting a new
> process or you just guess linux would swap because you don't see "free"
> memory in top output?
>
> Tanel.
>
> ----- Original Message -----
> From: Sai Selvaganesan
> To: Multiple recipients of list ORACLE-L
> Sent: Saturday, November 01, 2003 1:34 AM
> Subject: RE: memory usage by dbw very high
>
>
> rich
> the ipcs output shows 1.1 gb. so nearly 2 gb(total ram size is 3.08) is
> used by non shared memory size.
> i went thru all the processes and found dbwr using the max %mem. what
> could
> be the reason?
> sai
>
> "Jesse, Rich" <Rich.Jesse_at_qtiworld.com> wrote:
> If I'm not mistaken, this figure includes the size of the shared memory
> segment from the SGA. Take the output of the "oracle" line of "ipcs -a"
> (hopefully you'll only have one!) and subtract it from the process size
> to
> get a better idea of the non-shared memory size of the process.
>
> Rich
>
> Rich Jesse System/Database Administrator
> rjesse_at_qtiworld.com Quad/Tech Inc, Sussex, WI USA
>
>
> -----Original Message-----
> Sent: Friday, October 31, 2003 3:49 PM
> To: Multiple recipients of list ORACLE-L
>
>
> hi
>
> i have a system that has no active users at this point of time. the
> memory
> used by the dbw process is very high leading to a lot of swapping when
> any
> process starts.
> here are the spces
> version:9.2.0.4
> os:Linux 2.4.9-e.24smp
> o/p from top:
> 1:44pm up 29 days, 23:55, 4 users, load average: 1.73, 1.68, 1.35
> 132 proces! ses: 131 sleeping, 1 running, 0 zombie, 0 stopped
> CPU0 states: 24.4% user, 2.2% system, 0.0% nice, 72.2% idle
> CPU1 states: 0.5% user, 0.5% system, 0.0% nice, 98.0% idle
> CPU2 states: 0.0% user, 0.1% system, 0.0% nice, 99.4% idle
> CPU3 states: 0.3% user, 0.4% system, 0.0% nice, 98.3% idle
> Mem: 3089964K av, 3083380K used, 6584K free, 846848K shrd, 193448K
> buff
> Swap: 2048152K av, 1652K used, 2046500K free 1852468K
> cached
> sga size:
> Total System Global Area 1084823632 bytes
> Fixed Size 452688 bytes
> Variable Size 335544320 bytes
> Database Buffers 738197504 bytes
> Redo Buffers 10629120 bytes
> pga aggregate size:700M
> and ps o/p of dbw process
> USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
> oracle 4062 0.0 16.4 1131260 508168 ? S 10:16 0:06
> ora_dbw0_revenue
>
> please advise. what is really going on.
>
> thanks
> sai
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Jesse, Rich
> INET: Rich.Jesse_at_qtiworld.com
>
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Mladen Gogala
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Received on Sat Nov 01 2003 - 09:39:24 CST
