Two 12.1.0.2 database show different cost calculations mechanism for same query

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)

Thanks,
Yogi | Technical Specialist - Databases | Fidelity International FIL India Business Services Private Limited 5th Floor, Tower - D, Unitech Cyber Park, Sector 39, Gurgaon 122 002, Haryana, India. T: +91 124 412 3656 | I: 8 779 3656 | E: yogesh.tiwari_at_fil.com<mailto:yogesh.tiwari_at_fil.com> Disclaimer: The information transmitted is intended for the person or entity to which it is addressed and may contain confidential, privileged or copyrighted material or attorney work product. If you receive this in error, please contact the sender and delete the material from any computer. Any comments or statements made are not necessarily those of FIL India Business Services Private Limited or any other Fidelity entity. All e-mails may be monitored or recorded.

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