http://docs.oracle.com/cd/E11882_01/server.112/e25523/parallel003.htm#i1006520


The DDL statements that can be parallelized are there.


You might consider using a parallel CTAS (create table as select) or parallel INSERT /*+ append */ into a new table in another tablespace (and then indexing/constraining/etc and dropping old/renaming new)

You could do this online with dbms_redefinition as well.

The reasons you might want a rebuild into a new structure are two fold.

a) the column you are encrypting will be going from a varying length field (assuming number/varchar2) to a fixed width field that will be much larger than your existing column. For example, if you take a varchar2(30) and encrypt it - and the average length was 15 characters - it will now be a raw field under the covers with a fixed length of 32 bytes. That would likely cause a lot of row migrations if you just did the alter - the create/insert /*+ append */ would avoid that (and you can do that without any redo/undo generation as well if you like)

b) you want to try to get rid of the tablespace that contained this information anyway - because there will be remnants of this column in that tablespace (we do not zero things out necessarily). When encrypting data - you want to think about getting rid of the files that had unencrypted data in them (remember your backups, exports and archives too!)