SQL> create table t
  2  as select
  3       d.OWNER
  4      ,d.OBJECT_NAME
  5      ,d.SUBOBJECT_NAME
  6      ,rownum OBJECT_ID
  7      ,d.DATA_OBJECT_ID
  8      ,d.OBJECT_TYPE
  9      ,d.CREATED
 10      ,d.LAST_DDL_TIME
 11      ,d.TIMESTAMP
 12      ,d.STATUS
 13    from dba_objects d,
 14     ( select 1 from dual connect by level <= 20 );

Table created.

SQL>
SQL> create global temporary table gtt on commit preserve rows
  2  as select * from t where 1=0;

Table created.

--
-- So our "mat view" T has 1.5million rows in it.
--

--
-- we take a copy of what it is currently into a global temp table
--

SQL> insert /*+ APPEND */ into gtt select * from t;

1552240 rows created.

SQL> commit;

Commit complete.

--
-- Now here is our "mods" to the mat view which occurred as part of a refresh
--

SQL>
SQL> delete from t
  2  where owner like 'APEX%'
  3  and rownum <= 10000;

10000 rows deleted.

SQL>
SQL> insert into t
  2  select
  3       d.OWNER
  4      ,d.OBJECT_NAME
  5      ,d.SUBOBJECT_NAME
  6      ,-1*d.OBJECT_ID
  7      ,d.DATA_OBJECT_ID
  8      ,d.OBJECT_TYPE
  9      ,d.CREATED
 10      ,d.LAST_DDL_TIME
 11      ,d.TIMESTAMP
 12      ,d.STATUS
 13  from dba_objects d
 14  where rownum <= 10000;

10000 rows created.

--
-- Now I can do a full outer join to pick up 
-- deletes, inserts and updates
--

SQL> set timing on
SQL> select t.object_id, gtt.object_id
  2  from t
  3   full outer join gtt
  4   on ( t.object_id = gtt.object_id )
  5  where
  6    (  t.object_id is null or
  7       gtt.object_id is null or
  8       decode(t.owner,gtt.owner,1,0) = 0 or
  9       decode(t.object_name,gtt.object_name,1,0) = 0 or
 10       decode(t.subobject_name,gtt.subobject_name,1,0) = 0
          ...
          ...
 11    )
 12   /

20000 rows selected.

Elapsed: 00:00:03.55
SQL>