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CBC Latch contention in 10g

From: Smiley John - IL <SMILEYJ_at_tusc.com>
Date: Tue, 19 Oct 2004 15:31:24 -0500
Message-ID: <F5E885BEF9540D47A7BDC03CF168808709924B7D@tuscil_ex1>


I'm seeing large numbers of CBC latch waits when many sessions (20-40) run the same SELECT statement simultaneously (I can peek at v$session_wait and catch this many sessions waiting on latch free: cache buffers chains for the same sql_id).

CBC latch children have been sharable in read mode since 9i. I didn't see any DML taking place at the same time that would cause these latches to be taken in exclusive mode, so I'm wondering why they're blocking on the CBC latches. I've examined the CBC latch children with the most sleeps and examined the blocks on their hash chains and found exactly what I expected to find: hot blocks on some of the tables referenced in the queries. But if the latches are truly sharable for CR buffer gets, this shouldn't cause them to pile up on the latch. Assuming delayed block cleanout isn't the problem, what might explain this? I've searched MetaLink for latch related bugs in 10.1.0.2. No dice.

John Smiley

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Received on Tue Oct 19 2004 - 15:27:11 CDT

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