The Oracle database includes several features to allow moving data online, ie: without preventing users to access it when it is being moved (DML operation are not blocked).
One of those features is to change a table definition, using the package DBMS_REDEFINITION.
While moving a table is an online operation since version 12.2, redefinition is still needed for some changes. Also is needed in older versions.
In this session best practices will be shown based on experience of using it with big tablespaces, with examples covering all the steps needed to use DBMS_REDEFINITION under different scenarios, including the problems you can find, how to resolve them and how this process is different in version 11.2 and 12.