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Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
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Message Score Author Date
Agreed, this is not a new question but the introdu...... JB Koyen Sep 07, 2015, 13:48
Hi JB From what I have read, this limitation to...... Score: 600 PtsScore: 600 PtsScore: 600 PtsScore: 600 PtsScore: 600 Pts Jan Schnackenberg Sep 07, 2015, 14:34
Jan, Thanks, a valid point to investigate! R...... JB Koyen Sep 07, 2015, 15:25
Good point Jan! I work with servers where HT is...... Score: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 Pts Ales Kavsek Sep 08, 2015, 11:49
I have the same understanding, that this will not ...... Score: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 Pts Jan Schnackenberg Sep 08, 2015, 12:55
I created a topic on OraFAQ with a link to this ...... Score: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 Pts Michel Cadot Sep 08, 2015, 13:23
Thanks Michel for the link, indeed a good remark b...... Ales Kavsek Sep 08, 2015, 14:43
Jan, Ales, Michel, Thanks for the given feedbac...... JB Koyen Sep 08, 2015, 15:23
As far as I understand Hyperthreading as implement...... Score: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 Pts Jan Schnackenberg Sep 08, 2015, 17:47
Like always it is easier to qualify than to quanti...... JB Koyen Sep 08, 2015, 19:18

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Subject: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: JB Koyen, Belgium
Date: Sep 07, 2015, 13:48, 832 days ago
Os info: RHEL6
Oracle info: Oracle 12.1.0.2
Error info: n/a
Message: Agreed, this is not a new question but the introduction of SE2 by Oracle makes the question valid again.
Imagine running 12.1.0.2 SE2 running on a dual processor 8-core server.
Without hyper-threading there 2 x 8 = 16 CPU cores and with there 2 x 8 x 2 =32 logical CPU threads possible.

Because of the SE2 limitation of 16 CPU threads it wouldn't make much sense to enable hyper-threading.
This would be especially the case if hyper-threading could introduce an overhead.

But I don't have hard facts to decide if this reasoning is correct or flawed.

And what if one had a dual 6 core CPU of even a 12 core CPU, what would be the criteria?
I hear some one thinking, why don't you test these cases?
But that would be easier said than done.
If you can share your thoughts, I would really appreciate that!

JB
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: Jan Schnackenberg, Germany
Date: Sep 07, 2015, 14:34, 832 days ago
Score:   Score: 600 PtsScore: 600 PtsScore: 600 PtsScore: 600 PtsScore: 600 Pts
Message: Hi JB

From what I have read, this limitation to 16 threads affects foreground (user) sessions only. Since your database will always have a number of background sessions, using their own processes, hyperthreading might still bring a profit.

The reason is the smaller time needed for process switches.

Of course, as with some other situations, intuition might be far from reality.

Regards,
Jan
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: JB Koyen, Belgium
Date: Sep 07, 2015, 15:25, 832 days ago
Message: Jan,

Thanks, a valid point to investigate!

Regards,

RB
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: Ales Kavsek, Slovenia
Date: Sep 08, 2015, 11:49, 831 days ago
Score:   Score: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 Pts
Message: Good point Jan!

I work with servers where HT is purposely ("bad" app -> latch contention -> add more CPU's -> worse performance) turned off and some with HT turned on.

I think this post on Intel site covers the subject well:

https://communities.intel.com/community/itpeernetwork/datastack/blog/2013/08/23/hyper-threading-on-or-off-for-oracle

Also read the last paragraph!

So in general, I would likely turn HT on for SE2. As far as I understand, the limit is built in SE2 kernel itself, so having HT on (>16 threads) does not violate SE2 license.

Regards,
Ales
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: Jan Schnackenberg, Germany
Date: Sep 08, 2015, 12:55, 831 days ago
Score:   Score: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 Pts
Message: I have the same understanding, that this will not violate the SE2 licence.

The UPGRADE Blog by Mike Dietrich has the same discussion below this post: https://blogs.oracle.com/UPGRADE/entry/oracle_12_1_0_22

The linked blog post by Franck Pachot of dbi services is interesting, too: http://blog.dbi-services.com/oracle-standard-edition-two/

Regards,
Jan
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: Michel Cadot, France
Date: Sep 08, 2015, 13:23, 831 days ago
Score:   Score: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 Pts
Message:
I created a topic on OraFAQ with a link to this one.
John's remark and link are interesting.

http://www.orafaq.com/forum/t/198577/

Regards
Michel
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: Ales Kavsek, Slovenia
Date: Sep 08, 2015, 14:43, 831 days ago
Message: Thanks Michel for the link, indeed a good remark by John. I'm not sure if Intel behaves similarly, throttling individual threads, which can become a major issue for (non-parallel) applications that benefits from frequency rather than #CPU's.

Jan, thank you for the link to Franck post which lead me to another Mike Dietrich post "DBCA 12c and "datapatch.pl" - things to know", I learned something today ;-), and with the excellent timing, because tomorrow I'll attend Mike's one day seminar in LJ regarding diff. upgrade paths to 12c. :)

Regards,
Ales
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: JB Koyen, Belgium
Date: Sep 08, 2015, 15:23, 831 days ago
Message: Jan, Ales, Michel,

Thanks for the given feedback!
It seems that I have homework to do ;-)

Best regards,

JB
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: Jan Schnackenberg, Germany
Date: Sep 08, 2015, 17:47, 830 days ago
Score:   Score: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 PtsScore: 400 Pts
Message: As far as I understand Hyperthreading as implemented by Intel, this just presents a second set of CPU-registers as a virtual second CPU.

If this second CPU is not used (either because HT is off, or because the OS does not assign this CPU to any thread/process) then the remaining CPU will run as if there is only one CPU.

If the second CPU is assigned to another process, then the CPU will alternate between the assigned processes by switching the (visibility of the) register-contents with minimal overhead. Normally the registers would have to be saved and restored for each context switch. So this allows two threads to run a little faster on one CPU compared to the setup without HT.

There is nothing like a resource manager forcing the "virtual" HT-CPUs to each have 50% of the performance.

Regards,
Jan
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Subject: Re: Would it be useful to enable Hyper-Threading in Oracle 12.1.0.2 on Linux
Author: JB Koyen, Belgium
Date: Sep 08, 2015, 19:18, 830 days ago
Message: Like always it is easier to qualify than to quantify the differences.
And my handicap is that low level CPU architecture isn't really my cup of tea.
Actually, I don't have no idea what ballpark percentage to use as overhead for multi-threaded CPU cores.

From Jan I understand that Intel HT overhead is minimized.
But from the story of John for the Sparc it seems that it can have significant impact.
(See http://www.orafaq.com/forum/t/198577/ mentioned by Michel)

So, the way of the hardware implementation like the mentioned Sparc and Intel can makes a huge difference.
And the way the database is used will be important too. Many short transaction that can run parallel will favourite more threads. But a limited amount of long running queries are bound to there own thread and probably fine with use real cores(no parallel query in SE).

I hope that I can experience this in the near future first hand from our "workfloor"!

Regards & thanks,

JB
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