In the environment you describe, it makes sense that there aren 't any negatives to running parallel.
I think that the situation that Cary was describing, where there are lots of users, all trying to utilize parallel operations, is what folks need to look out for. If you have lots of users, enabling parallel operations is a good way to light your CPUs on fire and make the performance problems MUCH worse.
Parallel operation, by design, is a CPU hog. Instead of tuning, you 're saying, "I have a huge amount of work to do, so, let 's chop it up into little pieces and and do lots of little chunks of work at the same time, then glue it all back together. " That 's great if you have the CPU resources to spare. If you 've got a 8 (or even 16 or 32 or more) CPU box, but you 're supporting 100s of users, then the numbers may not work in your favor.
In your environment, with a small number of users, it 's not really an issue. You sohuld still consider though, depending on the types of queries you 're running, it still may be possible to tune SQL, turn off parallel, and get better performance. If you can tune the SQL and/or tune the app, and eliminate unnecessary work, that 's always going to be a win over ignoring the fact that you 're doing unnecessary work and using parallel operations to blast through that extra work.
-Mark
-- --Original Message-- --
From: oracle-l-bounce@(protected)
[mailto:oracle-l-bounce@(protected)]On Behalf Of Freeman, Donald
Sent: Tuesday, August 03, 2004 1:13 PM
To: oracle-l@(protected)
Subject: RE: Oracle 9.2.0.5 "10046 " Tracing Causes Server Crash on
Windows 2000?
We haven 't seen any negative results from using parallel. The db is a =
datawarehouse with no more than 4 concurrent users connecting through =
Cognos during the day and no activity at night outside the Informatica =
ETL process.=20
-- --Original Message-- --
From: oracle-l-bounce@(protected)
[mailto:oracle-l-bounce@(protected)]On Behalf Of Cary Millsap
Sent: Tuesday, August 03, 2004 12:09 PM
To: oracle-l@(protected)
Subject: RE: Oracle 9.2.0.5 "10046 " Tracing Causes Server Crash on
Windows 2000?
Bugs and other undocumented behaviors notwithstanding, using parallel
features produces one specific and very important risk that you should
understand.
When you N-way parallelize a process, you convert a single process into =
=3D
N
distinct processes (at least N--in Oracle, it 's actually 2N+1). Each of
these processes now competes for CPU time, memory busses, latches, =3D
locks,
and everything else that a process competes for. What I see so =3D
frequently is
the following...
What the user wants: My user action runs in 80 seconds, so I 'll 4-way
parallelize it in attempt to make it run in 20 seconds.
What really happens: Yesterday 100 users made 100 database connections =
=3D
at a
time, which used 80% of the CPU capacity on the server. Today, the same
users are making 900 database connections at a time (2*4+1 sessions for =
=3D
each
of the same 100 users). CPU utilization is locked perpetually at 100%, =
=3D
and
the system is deadlocked.
In many cases, the original 80-second user can be fixed to run in a =3D
second
or less by eliminating wasteful work. When this is the case, the end =3D
result
is that users are ecstatic about response time, and the next server =3D
upgrade
can be deferred by several months because the system is running at
significantly reduced CPU utilization.
So, what 's the best way to tune a parallel operation? Deactivate the
parallelization, and optimize the remaining serial operation. :)
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *
Upcoming events:
- Performance Diagnosis 101: 8/10 Boston, 9/14 San Francisco, 10/5 =3D
Charlotte
- SQL Optimization 101: 7/26 Washington DC, 8/16 Minneapolis, 9/20 =3D
Hartford
- Hotsos Symposium 2005: March 6-10 Dallas
- Visit www.hotsos.com for schedule details...
-- --Original Message-- --
From: oracle-l-bounce@(protected) =3D
[mailto:oracle-l-bounce@(protected)]
On Behalf Of Freeman, Donald
Sent: Tuesday, August 03, 2004 10:20 AM
To: oracle-l@(protected)
Subject: RE: Oracle 9.2.0.5 "10046 " Tracing Causes Server Crash on =3D
Windows
2000?
We were hoping to improve query performance with parallel although it =
=3D
=3D3D
may not be necessary in all circumstances. Regarding parallel is it =
=3D3D
better to pick and choose what activities are performed in parallel? I =
=3D
=3D3D
think we 've basically defaulted it on after our performance improved in =
=3D
=3D3D
the areas we were concerned about. What about V$PARAMETER error? Is =
=3D3D
that significant? It keeps showing up in the alert log.=3D3D20
We had two occassions last week when I had to reboot the server. The =
=3D
=3D3D
first was recorded in the logs I provided. The second was when I =3D3D
arrived in the morning Friday and couldn 't log in. I couldn 't find any =
=3D
=3D3D
errors recorded anywhere. We installed 9.2.0.5 on Tuesday the 27th.
-- --Original Message-- --
From: oracle-l-bounce@(protected)
[mailto:oracle-l-bounce@(protected)]On Behalf Of Tanel P=3D3DF5der
Sent: Tuesday, August 03, 2004 10:46 AM
To: oracle-l@(protected)
Subject: Re: Oracle 9.2.0.5 "10046 " Tracing Causes Server Crash on
Windows 2000?
It seems that, you are using parallel query and =3D3D
cursor_sharing=3D3D3Dforce|similar
here, it might be that the problem occurs when all of these features
"collide ". Do you need your query to run in parallel? (parallel option
triggers lots of bugs, including data/query result corruption ones, in =
=3D
=3D3D
my
experience).
Tanel.
-- -- Original Message -- --=3D3D20
From: "Freeman, Donald " <dofreeman@(protected) >
To: "Oracle-L (E-mail) " <oracle-l@(protected) >
Sent: Tuesday, August 03, 2004 5:26 PM
Subject: Oracle 9.2.0.5 "10046 " Tracing Causes Server Crash on Windows =
=3D
=3D3D
2000?
> I am finally getting to practice some of the tracing functionality =
=3D3D
that =3D3D3D
> is discussed here and ran into something I haven 't seen dicussed here. =
=3D
=3D3D
=3D3D3D
> We had a complaint about a query that performs inconsistently and I =
=3D
=3D3D
=3D3D3D
> enabled my session trigger on user logon to capture it. The server =
=3D
=3D3D
=3D3D3D
> failed at a point shown below. The first entry is the alert log =3D3D
entry. =3D3D3D
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