Re: memory usage by dbw very high

What we have here is a confusion with terminology. Process cannot "be swapping". When there is a serious shortage of memory, the swap demon (yes, your Unix box is haunted) known by the horrible name of [kswapd] writes the whole address space space belonging to the process onto swap. At that point, process is swapped. Unless, we are talking about the kswapd process, the process cannot "be swapping". Kernel swap demon seldomly uses oracle database. Process can be paging. When there is serious shortage of memory (but less serious then in the first case), pages are stolen from the process and written onto the swap. It's called "page replacement". When processes need pages that have been thrown out of memory by the page replacement demon (in case of Linux, it's called bdflush but on some unix implementations, there is a process called "updated" or "paged " which performs this function.), it pages them in. If the page is in memory (buffer cache would a good place to look), we're talking about the soft page fault. If the page has to be read from the disk, we're talking about hard page fault. Processes that page get charged for a lot of CPU time, all of it in the kernel mode. If you have gtop (my kindest advice is to get it), you can set preferences and see kernel mode for the processes. Ones consuming large amounts of the kernel mode are ones that are paging. On 11/03/2003 01:24:27 PM, Sai Selvaganesan wrote:
> hi tanel and mladen
> not every time a process is started does it swap but sometimes swapping does happen.(this is from the top o/p which shows a increase in the memory used in swap.).how do we check whether a single process swaps or not?
>
> and the dbw process is using more % of memory than a couple of days back.(o/p pf ps aux).
> is this how linux kernel works or is there something else i can check.
>
> thanks
> sai
> what is meant by OP,tanel..
>
>
> Tanel Poder <tanel.poder.003_at_mail.ee> wrote:
> Thanks Mladen, that was a good tip about linux kernel enhancement, however
> OP still uses 2.4.9 as stated in original post.
>
> I just wanted to know whether OP actually sees excessive paging or just
> memory being "full", the latter one, as you know, isn't really a problem.
>
> Tanel.
>
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L"
> Sent: Saturday, November 01, 2003 5:39 PM
>
>
> > 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" 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
> > Oracle DBA
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > --
> > Author: Mladen Gogala
> > INET: mgogala_at_adelphia.net
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> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Tanel Poder
> INET: tanel.poder.003_at_mail.ee
>
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Mladen Gogala
Oracle DBA

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Author: Mladen Gogala
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