Re: cas latch

I saw quite a few cas latch waits today, Oracle 9.2.0.4 on HP-UX 11.11PA-RiSC. Do these CPUs support CAS instructions?

I am not sure why I am having it. I will read about wikipedia and see what it is all about.

Thanks!

On 10/30/06, Bobak, Mark <Mark.Bobak_at_il.proquest.com> wrote:
>
> As K Gopalakrishnan mentioned, CAS latch is "Compare and Swap". My
> understanding is that, on *most* modern CPUs, the CAS instruction is
> built-in to the instruction set as an atomic operation. In those cases, you
> shouldn't see CAS latch used at all, cause Oracle can directly use the CAS
> instruction itself. In cases where the CPU does not support a CAS
> instruction, Oracle has implemented the CAS functionality in software. To
> support the atomicity of the CAS functionality in software, the CAS latch is
> utilized.
>
> -Mark
>
>
> ***--*
>
> *Mark J. Bobak*
>
> *Senior Oracle Architect*
>
> ***P****ro****Q****uest Information & Learning*
>
> There is nothing so useless as doing efficiently that which shouldn't be
> done at all. –Peter F. Drucker, 1909-2005
>
>
>
> ------------------------------
> *From:* oracle-l-bounce_at_freelists.org [mailto:
> oracle-l-bounce_at_freelists.org] *On Behalf Of *K Gopalakrishnan
> *Sent:* Monday, October 30, 2006 12:17 PM
> *To:* exriscer_at_gmail.com; oracle-l
> *Subject:* Re: cas latch
>
>
> Cheng,
>
> Do you see any contention for this latch?
>
> CAS is Compare and Select. Check
> http://en.wikipedia.org/wiki/Compare_and_swap for some details on CAS.
>
>
>
> Have a nice day !!
> ------------------------------------------------------------
> Best Regards,
> K Gopalakrishnan,
> Co-Author: Oracle Wait Interface: Oracle Press 2004.
> http://www.amazon.com/gp/product/007222729X/
>
> Author: Oracle Database 10g RAC Handbook, Oracle Press 2006
> http://www.amazon.com/gp/product/007146509X/
>
> ----- Original Message ----
> From: LS Cheng <exriscer_at_gmail.com>
> To: oracle-l <oracle-l_at_freelists.org>
> Sent: Monday, 30 October, 2006 8:43:47 AM
> Subject: cas latch
>
> Hi
>
> I was wondering if anyone know what does cas latch do? I know is a shared
> latch but not sure for what part of SGA?
>
> Thanks
>
>
>
>
>
>

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