RE: KCL gc element parent latch

From: Rajesh Rao <>
Date: Wed, 16 Dec 2009 12:34:13 -0500
Message-ID: <>

Thank you Tanel.

"so if you have lots of GC ops, these latches will be used. Fix the GC traffic and the latching problem will go away."

So, those waits would be an effect, rather than the cause leading to gc cr request waits. These waits themselves are not significant. We see fast object checkpoints as well as this KCL latch that seems to precede most of the gc cr request waits we see. We know the fix for the gc waits.

Thank you for the script. That goes into the same directory where I have the snapper one stored :)


From: Tanel Poder [] Sent: Wednesday, December 16, 2009 12:16 PM To: Rajesh Rao
Subject: Re: KCL gc element parent latch

GC operations may require changes to PCM locks / lock elements. The lock element array (V$GC_ELEMENT) is protected by gc element latches... so if you have lots of GC ops, these latches will be used. Fix the GC traffic and the latching problem will go away.

How significant % of your sessions response time is spent waiting for this latch?

If you see significant waits for that latch, you can run latchprofX to gain undersanding who are the main holders of these latches and which kernel functions cause the latches to be held the most etc:


On Wed, Dec 16, 2009 at 4:27 AM, Rajesh Rao <<>> wrote: RAC. Looking to get more insight into this latch as I see seek to troubleshoot and check for co-relation to an issue with sessions experiencing "gc cr request" waits. Especially, what causes sessions to wait on this latch?


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Tanel Poder

-- Received on Wed Dec 16 2009 - 11:34:13 CST

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