Re: High CPU usage

From: Gerry Miller <gerry_at_millerandbowman.com>
Date: Tue, 19 Jun 2012 09:05:05 +1000
Message-ID: <4FDFB421.4000408_at_millerandbowman.com>

 Hi Subodh
I can't create or rebuild online as it is Oracle Standard Edition.

The memory is 30G and the SGA 20G.

When memory usage increases there is no perceptible increase in PGA usage.

I perhaps did not make it clear that this issue is not just with index creation but also with any SQL being run; the tkprof example I gave below is from a basic query, which is one of many that uses a lot more CPU during one execution than another and yet performs no more buffer gets, has the same wait events etc.

Thanks and regards

Gerry

Subodh Deshpande wrote: can you rebuild indexes online..it should a lesser time.
if the size of these tables and indexes are bulk then it may take time, and rebuild on line will take lesser than dropping and recreating cpu 16 and memory usage is 97%, is whole of available memory is been allocated to SGA ! check pga size, are their any running long queries/sessions/transactions/Cartesian queries

On 13 June 2012 09:40, Gerry Miller <gerry_at_millerandbowman.com[1]> wrote:  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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Received on Mon Jun 18 2012 - 18:05:05 CDT