很多人都认为使用直接加载可以大量减少redo的产生量，实际上直接加载并非在任何时候都能减少redo的产生。如果对象实在LOGGING模式下，直接加载并不能显著的减少日志量。看一个例子：

sys@ORCL> create table t

2 as

3 select * from dba_objects where 1=0;

Table created.

sys@ORCL> alter table t logging;

Table altered.

sys@ORCL> alter table t logging;

Table altered.

sys@ORCL> set autotrace trace stat;

sys@ORCL> insert into t

2 select * from dba_objects where rownum<10000;

9999 rows created.

Statistics

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

910 recursive calls

937 db block gets

2710 consistent gets

1 physical reads

1052484 redo size

924 bytes sent via SQL*Net to client

973 bytes received via SQL*Net from client

6 SQL*Net roundtrips to/from client

5 sorts (memory)

0 sorts (disk)

9999 rows processed

sys@ORCL> rollback;

Rollback complete.

sys@ORCL> insert/*+append*/ into t

2 select * from dba_objects where rownum<10000;

9999 rows created.

Statistics

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

40 recursive calls

139 db block gets

2283 consistent gets

28 physical reads

1030572 redo size

908 bytes sent via SQL*Net to client

987 bytes received via SQL*Net from client

6 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

9999 rows processed

我们可以看到当表属性为LOGGING属性时，传统加载和直接加载所产生的redo量并没有很大的差别。主要原因是：当一个表为LOGGING属性时，即使是直接加载，所有改变的数据依然要差生redo，以便于以后的恢复，这时候直接加载并没有什么优势。

直接加载最常见是和NOLOGGING一起使用，这时候就能有效的减少redo量。例子：

sys@ORCL> rollback;

Rollback complete.

sys@ORCL> alter table t nologging;

Table altered.

sys@ORCL> insert/*+append*/ into t

2 select * from dba_objects where rownum<10000;

9999 rows created.

Statistics

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

182 recursive calls

128 db block gets

2292 consistent gets

22 physical reads

588 redo size

908 bytes sent via SQL*Net to client

987 bytes received via SQL*Net from client

6 SQL*Net roundtrips to/from client

5 sorts (memory)

0 sorts (disk)

9999 rows processed

在这种情况下直接加载的数据库不产生redo的，只有一些其他改变的数据产生一些redo，比如空间分配需要修改字典表或者修改段头数据块，这些修改会产生少量的redo.