Oracle 11g Fast Add Column Taking 11 Hours
Ok, I sacrificed one of my 10.2 sandbox databases for a good cause, and upgraded it to 11.2.

As I suspected, the above DDL optimization does not work with compatible parameter still set to '10.2.*'.

After increasing compatible parameter, it works as intended:

SQL&gt; show parameter compa

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
cell_offload_compaction              string      ADAPTIVE
compatible                           string      10.2.0.5.0
plsql_v2_compatibility               boolean     FALSE

SQL&gt; alter table t1 add C_DDL number default 42 not null;

Table altered.

Elapsed: 00:00:52.85
SQL&gt; alter system set compatible='11.2.0.0.0' scope=spfile;

System altered.

Elapsed: 00:00:00.00

SQL&gt; shu immediate
startup
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL&gt; ORACLE instance started.

Total System Global Area 1068937216 bytes
Fixed Size                  2260088 bytes
Variable Size             289407880 bytes
Database Buffers          771751936 bytes
Redo Buffers                5517312 bytes
Database mounted.
Database opened.

SQL&gt; alter table t1 add D_DDL number default 42 not null;

Table altered.

Elapsed: 00:00:00.04