RE: cas latch

From: Bobak, Mark <Mark.Bobak_at_il.proquest.com>
Date: Mon, 30 Oct 2006 12:34:24 -0500
Message-ID: <AA29A27627F842409E1D18FB19CDCF270A1D4EDC@AABO-EXCHANGE02.bos.il.pqe>

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

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: 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

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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http://www.freelists.org/webpage/oracle-l Received on Mon Oct 30 2006 - 11:34:24 CST