Oracle中关于insert中使用/*+append*/和nologging的总结

关于Nologging和append,一直存在很多误解，经过一系列研究,终于发现了Nologging的真相，

我们来看一下：

1.对于logging 的table处理

a.非归档模式下:

SQL> archive log list;

Database log mode              No Archive Mode

Automatic archival             Enabled

Archive destination            /opt/oracle/oradata/hsjf/archive

Oldest online log sequence     155

Current log sequence           157

SQL> @redo

SQL> create table test as select * from dba_objects where 1=0;

Table created.

SQL> select * from redo_size;

     VALUE

----------

     63392

SQL> insert into test select * from dba_objects;

10470 rows created.

SQL> select * from redo_size;

     VALUE
----------

   1150988

SQL> insert /*+ append */ into test select * from dba_objects;

10470 rows created.

SQL> select * from redo_size;

     VALUE

----------

   1152368

SQL> select (1152368 -1150988) redo_append,(1150988 -63392) redo from dual;

REDO_APPEND       REDO

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

       1380    1087596

SQL> drop table test;

Table dropped.  

我们看到在Noarchivelog模式下,对于常规表的insert append只产生少量redo

b.归档模式下

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.

Total System Global Area  235999908 bytes

Fixed Size                   451236 bytes

Variable Size             201326592 bytes

Database Buffers           33554432 bytes

Redo Buffers                 667648 bytes

Database mounted.

SQL> alter database archivelog;

Database altered.

SQL> alter database open;

Database altered.

SQL> @redo

SQL> create table test as select * from dba_objects where 1=0;

Table created.

SQL> select * from redo_size;

     VALUE
----------

     56288

SQL> insert into test select * from dba_objects;

10470 rows created.

SQL> select * from redo_size;

     VALUE

----------

   1143948

SQL> insert /*+ append */ into test select * from dba_objects;

10470 rows created.

SQL> select * from redo_size;

     VALUE
----------

   2227712

SQL> select (2227712 -1143948) redo_append,(1143948 -56288) redo from dual;

REDO_APPEND       REDO

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

    1083764    1087660

SQL> drop table test;

Table dropped.  

我们看到在归档模式下,对于常规表的insert append产生和insert同样的redo
此时的insert append实际上并不会有性能提高.
但是此时的append是生效了的

通过Logmnr分析日志得到以下结果:

SQL> select operation,count(*)

  2  from v$logmnr_contents

  3  group by operation;

OPERATION                          COUNT(*)

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

COMMIT                                   17

DIRECT INSERT                         10470  

INTERNAL                                 49

START                                    17

                                          1   

我们注意到这里是DIRECT INSERT,而且是10470条记录,也就是每条记录都记录了redo.

2.对于Nologging的table的处理

a.非归档模式下

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.

Total System Global Area  235999908 bytes

Fixed Size                   451236 bytes

Variable Size             201326592 bytes

Database Buffers           33554432 bytes

Redo Buffers                 667648 bytes

Database mounted.

SQL> alter database noarchivelog;

Database altered.

SQL> alter database open;

Database altered.

SQL> @redo

SQL> create table test nologging as select * from dba_objects where 1=0;

Table created.

SQL> select * from redo_size;

     VALUE
----------

     56580

SQL> insert into test select * from dba_objects;

10470 rows created.

SQL> select * from redo_size;

 
     VALUE

----------

   1144148

SQL> insert /*+ append */ into test select * from dba_objects;

10470 rows created.

SQL> select * from redo_size;

     VALUE

----------

   1145528

SQL> select (1145528 -1144148) redo_append,(1144148 -56580) redo from dual;

REDO_APPEND       REDO

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

       1380    1087568

同样只有append才能减少redo的生成.

b. 归档模式下

SQL> create table test nologging as select * from dba_objects where 1=0;

Table created.

SQL> select * from redo_size;

     VALUE

----------

   2270284

SQL> insert into test select * from dba_objects;

 
10470 rows created.

SQL> select * from redo_size;

     VALUE

----------

   3357644

SQL> insert /*+ append */ into test select * from dba_objects;

10470 rows created.

SQL> select * from redo_size;

     VALUE

----------

   3359024

SQL> select (3359024 -3357644) redo_append,(3357644 - 2270284) redo from dual;

REDO_APPEND       REDO

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

       1380    1087360

SQL> drop table test;

Table dropped.

我们注意到,只有append才能减少redo

补充：

如果数据库开启了强记日志模式，在表上修改nologging是没有用的。

开启强记日志模式
SQL> alter database force logging;

SQL> select force_logging from v$database;

FOR
---
YES

关闭强记日志模式
SQL> alter database no force logging;

SQL> select force_logging from v$database;

FOR
---
NO

查看普通表的logging状态

SQL>select table_name,logging from dba_tables;

查看分区表的logging状态

SQL>select table_name,logging from dba_tab_partitions;

总结	非归档	归档
Logging	产生大量日志	产生大量日志
Nologging	产生大量日志	产生大量日志
Append	产生少量日志	产生大量日志
Append+Nologing	产生少量日志	产生少量日志

 

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