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Latch gets and CPU usage

From: Kristian Myllymäki <kristian_at_kmja.com>
Date: Mon, 15 May 2006 10:28:46 +0200 (CEST)
Message-ID: <59587.212.247.9.194.1147681726.squirrel@glenlivet.oderland.com>


Hi List,

I'm having a problem with high CPU usage that has escalated during the last week. The SQL causing this is already tuned to the best possible with the current design.

When I look at a tkprof summary of the trace file, it shows high 'latch free' waits compared to the total CPU usage. Since latch gets consume CPU, are they included under the 'CPU used by this session' statistic?

For instance, the tkprof summary below shows 1.86 seconds of CPU, and a 'latch free' wait time of 1.10 seconds. Does this mean that 59% (1.10 / 1.87) of the CPU resources used by this query comes from latch gets? Just so I can be sure if this problem is caused by latch contention.

My first guess would be that when a process goes to sleep from consequtive latch misses, the wait time will increase but not the 'CPU used' statistic? If so, is there any way to know how much CPU resources my latch misses are consuming?

I'm running 9.2.0.6.

call count cpu elapsed disk query current  rows
------- ------ -------- ---------- ---------- ---------- ----------



Parse 1 0.00 0.00 0 0 0

    0
Execute 1 0.01 0.00 0 0 0

    0
Fetch 49 1.86 19.40 0 38779 0   483
------- ------ -------- ---------- ---------- ---------- ----------



total 51 1.87 19.41 0 38779 0   483

Misses in library cache during parse: 0
Optimizer goal: CHOOSE
Parsing user id: 40

Elapsed times include waiting on following events:

  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                      50        0.00          0.00
  SQL*Net message from client                    50        0.10          0.32
  latch free                                     16        0.48          1.10
********************************************************************************


Thanks,

/Kristian

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http://www.freelists.org/webpage/oracle-l Received on Mon May 15 2006 - 03:28:46 CDT

Original text of this message

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