RE: cas latch

Why am I not surprised?  If I recall correctly, the HP RISC arctitecture
is one that does not support the CAS instruction, at least on some of
the older CPUs.  Not sure if that is still true for it's most recent CPU
offerings.
 
-Mark
 

--

Mark J. Bobak

Senior Oracle Architect

ProQuest Information & Learning

There is nothing so useless as doing efficiently that which shouldn't be
done at all.  -Peter F. Drucker, 1909-2005

 

________________________________

From: LS Cheng [mailto:exriscer@xxxxxxxxx] 
Sent: Monday, October 30, 2006 1:18 PM
To: Bobak, Mark
Cc: kaygopal@xxxxxxxxx; oracle-l
Subject: Re: cas latch


I saw quite a few cas latch waits today, Oracle 9.2.0.4 on HP-UX 11.11
PA-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@xxxxxxxxxxxxxxx> 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 roQ uest Information & Learning

        

        There is nothing so useless as doing e fficiently that which
shouldn't be done at all.   -Peter F. Drucker, 1909-2005

        

         

________________________________

        From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:
oracle-l-bounce@xxxxxxxxxxxxx <mailto:oracle-l-bounce@xxxxxxxxxxxxx> ]
On Behalf Of K Gopalakrishnan
        Sent: Monday, October 30, 2006 12:17 PM
        To: exriscer@xxxxxxxxx; 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@xxxxxxxxx <mailto:exriscer@xxxxxxxxx>
>
        To: oracle-l <oracle-l@xxxxxxxxxxxxx>
        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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