High CPU usage
- From: Gerry Miller <gerry@xxxxxxxxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 13 Jun 2012 14:10:05 +1000
Hi
I am performing regression tests on index creation on Oracle Standard
Edition10.2.0.4 in RHEL 5.3. The first time I created the 450 indexes it
took 16 hours. A few days later I dropped them and recreated them and it
took 30 hours. I did it a third time and it is still running after 50
hours,with only 320 indexes created. I enabled tracing during the second
runand have found that the time is virtually all down to CPU usage. Buffer
gets are about the same and a resource profile show that CPU accounts for
86% of resource usage and scattered reads 8%. There are no other significant
waits and the 16 CPUs on the server are running at around 85% idle all the
time, while memory usage is quite high at 97%.
Furthermore, in comparing my regression test results I have found that CPU
usage is consistently and significantly higher in one result set than
others. For example, consider this one tkprof output:
First Run: call count cpu elapsed disk query
current rows
------- ------ -------- ---------- ---------- ---------- ----------
----------
Parse 1 0.00 0.00 0 0 0
0
Execute 1 0.00 0.00 0 0 0
0
Fetch 5 0.00 0.00 0 55 0
50
------- ------ -------- ---------- ---------- ---------- ----------
----------
total 7 0.00 0.00 0 55 0
50
Second Run: call count cpu elapsed disk query
current rows
------- ------ -------- ---------- ---------- ---------- ----------
----------
Parse 1 0.00 0.00 0 0 0
0
Execute 1 32.74 31.98 0 0 0
0
Fetch 5 0.00 0.00 0 55 0
50
------- ------ -------- ---------- ---------- ---------- ----------
----------
total 7 32.74 31.99 0 55 0
50
This is for the same query, with the same execution plan, no ORDER BY clause
and the only waits events are 5 'SQL*Net message to/from client'
corresponding to the FETCHes. Why would it take 32 seconds the second time,
all down to CPU, when it is doing no sorting or extra buffer gets?
In my test results find hundreds of SQL statements that have the same
execution plans and comparable buffer get counts but the CPU time is MUCH
higher in one run than the other.
Does anyone have any suggestions as to what might be the cause of this
behaviour?
Thanks and Regards
Gerry Miller
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