These sections describe compatibility, upgrading, downgrading, and installation topics for Oracle Database 12c Release 2 (12.2).
Oracle REST Data Services (ORDS)
JDK7 is the minimum Java version for Oracle REST Data Services (ORDS).
Core Dump ORA-00600  Error Encountered After Database Upgrade
A core dump
ORA-00600  error is encountered after the database is upgraded to Oracle Database 12c Release 2 (12.2) and then downgraded back to its original release (reference Bug 20898997).
Always apply the patch for this bug before upgrading the database to Oracle Database 12c Release 2 (12.2).
Downgrading Oracle Database 12c Release 2 (12.2) to Oracle Database 11g Release 2 (18.104.22.168) Results in Errors When Running utlrp.sql
If SQLJ types are present when downgrading from Oracle Database 12c Release 2 (12.2) to Oracle Database 11g Release 2 (22.214.171.124), then the following
ORA-00600 error can occur when running
utlrp.sql to recompile invalid objects after running
catrelod.sql (reference Bug 16230705):
ORA-00600: internal error code, arguments: 
Apply the patch for this bug and recompile the type using the
ALTER TYPE COMPILE statement.
Select Product Languages Screen Missing in Oracle Client
Starting with Oracle Database 12c Release 2 (126.96.36.199), the Select Product Languages screen has been removed and Oracle Universal Installer installs all supported language files irrespective of the operating system locale (reference Bug 18223148).