Re: UNIX nice Command Good/Bad

Not sure if this has been mentioned some where, but it used to be that UNIX would lower priority of processes that had accumulated a lot of CPU time. So the Oracle Background processes would get lower priority over time. Stopping and starting an instance will fix this again ;-)

Cary Millsap wrote:

>Anything that an OS does to raise or lower process priority without the
>Oracle kernel's knowing is a bad thing.
>
>Example: An inefficient process called L that makes way too many cache
>buffer chains acquisitions is demoted ("nice"d to a less important
>priority). An important job called H that needs some of the same latches
>is promoted ("nice"d to a more important priority). L, which gets some
>user-mode CPU time in spite of its poor priority, works long enough to
>acquire a latch, and then it gets preempted. Now, when H needs the same
>latch that L is holding, H will consume lots of CPU spinning for the
>latch, but of course H can never obtain the latch until L releases it.
>But L is asleep most of the time because it has a low priority. You'll
>have a busy-looking system (high CPU utilization because of H's
>spinning), but nobody will be able to get anything done.
>
>When the Oracle kernel provides process prioritization or suspend/resume
>capabilities, it'll be fantastic (I think they advertise some of this
>stuff in 9i, but I'm not sure it works yet). But no OS can do the job
>unless it takes into account some of the things that Oracle is doing
>internally.
>
>
>Cary Millsap
>Hotsos Enterprises, Ltd.
>http://www.hotsos.com
>
>Upcoming events:
>- Hotsos Clinic, Oct 1-3 San Francisco, Oct 15-17 Dallas, Dec 9-11
>Honolulu
>- 2003 Hotsos Symposium on OracleR System Performance, Feb 9-12 Dallas
>- Next event: NCOAUG Training Day, Aug 16 Chicago
>
>
>
>-----Original Message-----
>Ethan
>Sent: Tuesday, August 06, 2002 5:23 PM
>To: Multiple recipients of list ORACLE-L
>
>There is an article on Metalink that talks about doing this and doesn't
>mention the problem but I will take your word over that. Another post
>on
>usenet talked about some different software available on particular
>operating systems that would do the smae thing as "nice" but I guess it
>does
>is a little more "nicley". Would this be safe? How about punishing the
>whole lot and forcing all processes with a particular database to run at
>a
>lower level?
>
>Ethan Post
>(972) 577-6552
>Ethan.Post_at_ps.net
>perotdba (AIM), epost1 (Yahoo)
>--------------------------------------------------------------------
>
>
>-----Original Message-----
>Sent: Tuesday, August 06, 2002 4:28 PM
>To: Multiple recipients of list ORACLE-L
>
>
>Still true.
>
>
>Cary Millsap
>Hotsos Enterprises, Ltd.
>http://www.hotsos.com
>
>Upcoming events:
>- Hotsos Clinic, Oct 1-3 San Francisco, Oct 15-17 Dallas, Dec 9-11
>Honolulu
>- 2003 Hotsos Symposium on OracleR System Performance, Feb 9-12 Dallas
>- Next event: NCOAUG Training Day, Aug 16 Chicago
>
>
>
>-----Original Message-----
>Ethan
>Sent: Tuesday, August 06, 2002 3:58 PM
>To: Multiple recipients of list ORACLE-L
>
>Is this still true?
>
>************************************************************************
>****
>*
>WARNING: do not run Oracle processes at different priority by altering
>the nice value. This is specifically warned against in the manuals.
>If you have a process with a lowered priority that obtains a lock on
>an object, then can't run because of the low priority, you will create
>a deadlock or hang situation. All Oracle processes should run at the
>same priority.
>
>

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