A developer reported an Oracle famous error ORA-00600 like the following:
java.sql.SQLException: ORA-00600: internal error code, arguments: [kclcls_2], , 
ORA-00600 is an internal error which is caught but unable to be handled by Oracle instance, the most important hint is the first argument in the error message, you can use it to lookup the true cause on MOS. To use ORA-00600 and ORA-07445 look-up tool, you need an Oracle account to access MOS.
In this case, the first arguments kclcls_2 in this case.
Generally speaking, ORA-00600 broadly covers many situations, we may have no idea what's going on even though we checked the look-up tool of ORA-00600. Most likely, they are bugs. Many other patterns of ORA-00600 error can be found below:
As for me, I clear the memory of both instances of a RAC system instead of restarting database to solve the error.
SQL> alter system flush shared_pool;
Maybe, we should search for a real solution later.