You have 2 possible resorts:

1. Prayers
2. Oracle Support

Given my recent experience with Oracle Support, I would recommend prayers.

Hi All,  Oracle version is -  12.1.0.2.0 and its Exadata. I am seeing Ora-600 while fetching explain plan through "set autotrace traceonly explain". Even explain plan for "Select 1 from dual" is working but that is also taking ~2minutes and that too failing with the same Ora-600 for other queries. I got a related bug from mos, but the work around which is provided as setting "_optimizer_push_pred_cost_based" to false is also not working, which means we are hitting some other bug. Has anybody encountered such a scenario?

Explain Plan for Query Errors with 'ORA-00600: internal error code, arguments: [KGL-heap-size-exceeded]' (Doc ID 2469727.1)

SQL> select 1 from dual;

Execution Plan

----------------------------------------------------------

ERROR:

ORA-00600: internal error code, arguments: [ktrenvchk_1], [0], [1], [0], [1],

[0], [0], [0], [], [], [], []

SP2-0612: Error generating AUTOTRACE EXPLAIN report

-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com