RE: CBC Latch contention in 10g

I believe Steve Adams once told me that the shareable latch feature is = not
implemented on HP-UX.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
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-----Original Message-----
From: oracle-l-bounce_at_freelists.org =
[mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of Smiley John - IL
Sent: Tuesday, October 19, 2004 3:31 PM
To: 'Oracle-L (E-mail)'
Subject: CBC Latch contention in 10g

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.=20

John Smiley

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