Can You Set a Datafile's Maxbytes / Maxsize to Less Than its Actual Size?

I was dealing with a message like this for one of our developers:

ORA-01653: unable to extend table ...

He was using a tablespace which had one datafile with AUTOEXTEND ON and this datafile had reached its MAXBYTES / MAXSIZE. I wondered what would happen if you tried to set a datafile's MAXBYTES / MAXSIZE to a value less than its actual size. I tried this first on Oracle 9. I started with a datafile which had an actual size of 20 megabytes and a MAXBYTES / MAXSIZE of 50 megabytes. I found that I was able to set its MAXBYTES / MAXSIZE to 1 megabyte and that the change was recorded in DBA_DATA_FILES:

SQL> select file_id, bytes, maxbytes, autoextensible

  2  from dba_data_files

  3  where tablespace_name = 'USER_DATA'

  4  /

 

   FILE_ID      BYTES   MAXBYTES AUT

---------- ---------- ---------- ---

        22   20971520   52428800 YES

 

SQL> alter database datafile 22

  2  autoextend on

  3  maxsize 1m

  4  /

 

Database altered.

 

SQL> select file_id, bytes, maxbytes, autoextensible

  2  from dba_data_files

  3  where tablespace_name = 'USER_DATA'

  4  /

 

   FILE_ID      BYTES   MAXBYTES AUT

---------- ---------- ---------- ---

        22   20971520    1048576 YES

 

SQL>

However, when I tried to do a similar thing in Oracle 11, the MAXBYTES value shown in DBA_DATA_FILES did not go below the actual size of the datafile:

SQL> select file_id, bytes, maxbytes

  2  from dba_data_files

  3  where tablespace_name = 'USERS'

  4  /

 

   FILE_ID      BYTES   MAXBYTES

---------- ---------- ----------

         4   20971520   52428800

 

SQL> alter database datafile 4

  2  autoextend on maxsize 10m

  3  /

 

Database altered.

 

SQL> select file_id, bytes, maxbytes

  2  from dba_data_files

  3  where tablespace_name = 'USERS'

  4  /

 

   FILE_ID      BYTES   MAXBYTES

---------- ---------- ----------

         4   20971520   20971520

 

SQL>