RE: Two 12.1.0.2 database show different cost calculations mechanism for same query

"Explain Plan Lies".
"Explain Plan Will Lie More Frequently In 12c".

12c has more Adaptives, more Evolutions.

Look at actual runtime statistics for the SQL, for multiple executions of the SQL to see if it is adapting / evolving !

NUM_ROWS may be the same. If you did Export-Import, CLUSTERING_FACTOR may be different. System Statistics may be different.

Cost in Gs and Ts would normally mean something drastic. In the old days it would be a missing join. I presume you are sure that the submitted SQLs are exactly the same in SIT and PROD. Did you compare the 10053 Traces in SIT and PROD and identify the differences ?

Hemant K Chitale

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Tiwari, Yogesh Sent: Thursday, December 10, 2015 1:33 PM To: 'oracle-l_at_freelists.org'
Cc: Tiwari, Yogesh
Subject: Two 12.1.0.2 database show different cost calculations mechanism for same query

Hi,

We recently upgraded to 12.1.0.2 from 11.2.0.3 on linux x86-64. Apart from all kinds of perf issues that we are fixing/struggling with, I found another strange behaviour.

Same query that runs in SIT env, has cost in few Gs, while same query in UAT has cost of few thousands. I went through 10053 trace, and found query in SIT is using additional CPU costing, along with IO costing, while same query in UAT is only using IO costing (akin to 11g) mechanism.

All tables involved are same, in both DBs, and have almost (99%) same num_rows.

Are we hitting some bug? Is it expected behaviour?

In same UAT for other queries(ones we investigated as part of perf issues), we see they too have huge cost compared to 11g cost. Huge here means, 11g cost was in few thousands, and 12c cost is in Gs and Ts :(

---Same patches are applied in SIT and UAT--- This is a DWH system $ORACLE_HOME/OPatch/opatch lspatches

18747342;
18961555;
21463894;
19141838;
20877664;
18966843;
21611406;OCW Interim patch for 21611406
19509982;
20373598;
21068507;Database PSU 12.1.0.2.4, Oracle JavaVM Component (Jul2015)
20831110;Database Patch Set Update : 12.1.0.2.4 (20831110)

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---

Thanks,
Yogi | Technical Specialist - Databases | Fidelity International
FIL India Business Services Private Limited
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