Oracle DB: 22.214.171.124
While running one select query it was failing with below exception.
ORA-10173: Dynamic Sampling time-out error
ORA-07445: exception encountered: core dump [qcdlgcd()+70] [SIGSEGV] [ADDR:0x4] [PC:0xCDFB0E6] [Address not mapped to object] 
Seeing the ORA-10173, I initially thought it might be the issue with dynamic sampling triggered by sql plan directive, I have gathered stats on the table which didn’t work.
Later disabled dynamic sampling at the session level to verify , query again failed with ORA-07445
Later came across oracle MOS note 2028777.1 mentioning to set the hidden parameter to false.
alter session set “_index_join_enabled”=false;
My symptoms for the issue are same after enabling the 10053 trace and checking the _index_join_enabled parameter.
ORA-07445: core dump [qcdlgcd()+70] for Union All Statement : No More Data To Read From Socket (Doc ID 2028777.1)
ORA-10173: Dynamic Sampling time-out error in alert.log (Doc ID 1491818.1)
Web application was not working, when connecting through ODBC application team is getting error ORA-28040 .
What Was changed:
Oracle database upgraded from oracle 126.96.36.199 to 188.8.131.52
SQLNET.ALLOWED_LOGON_VERSION default is changed to 11 from 8 in earlier versions. We need to modify the parameter to value 9 or less. SQLNET.ALLOWED_LOGON_VERSION is depreciated in 12c, SQLNET.ALLOWED_LOGON_VERSION_SERVER and SQLNET.ALLOWED_LOGON_VERSION_CLIENT replaced this parameter.
Schema export form system user failed with below errors.
Estimate in progress using BLOCKS method…
ORA-39126: Worker unexpected fatal error in KUPW$WORKER.CONFIGURE_METADATA_UNLOAD [ESTIMATE_PHASE]
ORA-01422: exact fetch returns more than requested number of rows
ORA-06512: at “SYS.DBMS_SYS_ERROR”, line 95
ORA-06512: at “SYS.KUPW$WORKER”, line 9001
—– PL/SQL Call Stack —–
object line object
handle number name
4069d2ac0 20462 package body SYS.KUPW$WORKER
4069d2ac0 9028 package body SYS.KUPW$WORKER
4069d2ac0 6814 package body SYS.KUPW$WORKER
4069d2ac0 13688 package body SYS.KUPW$WORKER
4069d2ac0 2654 package body SYS.KUPW$WORKER
4069d2ac0 9697 package body SYS.KUPW$WORKER
4069d2ac0 1775 package body SYS.KUPW$WORKER
4053c83e8 2 anonymous block
There was a DUAL table created under SYSTEM user having multiple rows.
SQL> select table_name,owner from dba_Tables where table_name=’DUAL’;
SQL> select * from dual;
Dropped the custom dual table created under system and the export worked fine.
drop table system.dual;