ORACLE Nologging相关知识
1) Nologging跟数据库的运行模式有关，8i和9i的默认安装都是非归档模式，并且自动归档默认是禁用
SQL> archive log list;
Database log mode No Archive Mode
Automatic archival Unabled
Archive destination C:/oracle/ora92/RDBMS
Oldest online log sequence 85
Current log sequence 87
2)关闭数据库
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
3)
SQL> startup mount
ORACLE instance started.
Total System Global Area 135338868 bytes
Fixed Size 453492 bytes
Variable Size 109051904 bytes
Database Buffers 25165824 bytes
Redo Buffers 667648 bytes
Database mounted.
4)修改为归档模式
SQL> alter database archivelog;
Database altered.
5)打开数据库
SQL> alter database open;
Database altered.
6)
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Unabled
Archive destination C:/oracle/ora92/RDBMS
Oldest online log sequence 85
Next online log sequence 87
Current log sequence 87
7)由于Automatic archivalà Unabled
SQL> archive log start;
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination C:/oracle/ora92/RDBMS
Oldest online log sequence 85
Next online log sequence 87
Current log sequence 87
8)此时推荐关闭数据库，然后进行一下备份
SQL> shutdown immediate
9)
SQL> startup
10)如果在9i环境中并设置了FORCE LOGGING，则nologging操作是无效的，并不会加快，可以通过如下语句设置为NO FORCE LOGGING。
SQL>Alter database no force logging;
是否开启了FORCE LOGGING，可以用如下语句查看
SQL> select force_logging from v$database;
FORCE_
------
NO
11) 一个使用CTAS nologging并比较redo size的例子
SQL> CREATE OR REPLACE VIEW redo_size
2 AS
3 SELECT VALUE
4 FROM v$mystat, v$statname
5 WHERE v$mystat.statistic# = v$statname.statistic#
6 AND v$statname.NAME = 'redo size';
View created.
SQL> connect sys/sys@oratest as sysdba;
SQL> create table t nologging as select * from dba_objects;
Table created.
--T产生的Redo
SQL> select * from redo_size;
VALUE
----------
48504
SQL> create table tt as select * from dba_objects;
Table created.
SQL> select * from redo_size;
VALUE
----------
3457796
--TT产生的Redo
SQL> select 3457796 - 48504 from dual;
3457796-48504
-------------
3409292
SQL> select table_name,logging from dba_tables where table_name in ('T','TT');
TABLE_NAME LOGGIN
------------------------------------------------------------ ------
T NO
TT YES
参考来源：http://www.itpub.net/showthread.php?s=&threadid=609347&perpage=10&pagenumber=2
12)index上使用nologging属性的例子
--创建Table T
colm@COLM> create table t as select * from all_objects;
colm@COLM> connect colm/colm@colm
已连接。
--查看一下当前redo size
colm@COLM> @c:/script/mystat "redo size";
colm@COLM> set echo off
NAME VALUE
--------------------------
redo size 560
--创建一个索引
colm@COLM> create index t_idx on t(object_name);
--查看一下此时redo size
colm@COLM> @c:/script/mystat "redo size";
colm@COLM> set echo off
NAME VALUE
--------------------------------
redo size 1252680
--重建该index
colm@COLM> alter index t_idx rebuild；
索引已更改。
--与之前的产生的redo size进行比较，V代表目前的redo ,Diff代表重建所产生的redo,可以发现creat index与alter index产生的redol量基本相等
colm@COLM> @c:/script/mystat2
colm@COLM> set echo off
NAME- V DIFF
---------- ------------------------------------------
redo size 2511720 1,259,040
--alter index nologging
colm@COLM> alter index t_idx nologging;
索引已更改。
colm@COLM> @c:/script/mystat2;
colm@COLM> set echo off
NAME V DIFF
---------- ------------------
redo size 2515968 2,124
--再一次重建索引,45K的redo size与之前的 1.2M 相比少了许多
colm@COLM> alter index t_idx rebuild;
索引已更改。
colm@COLM> @c:/script/mystat2;
colm@COLM> set echo off
NAME V DIFF
---------- ------------------
redo size 2559308 45,464
附：上面用到的2个脚本
--mystat.sql
set echo off
set verify off
column value new_val V
define S="&1"
set autotrace off
select a.name, b.value
from v$statname a, v$mystat b
where a.statistic# = b.statistic#
and lower(a.name) like '%' || lower('&S')||'%'
/
set echo on
--mystat2.sql
set echo off
set verify off
column diff format a18
select a.name, b.value V, to_char(b.value-&V,'999,999,999,999') diff
from v$statname a, v$mystat b
where a.statistic# = b.statistic#
and lower(a.name) like '%' || lower('&S')||'%'
/
set echo on
13）关于Direct insert append产生redo量的问题， eygle有做过测试
a). 数据库运行在非归档模式下:
create table test as select * from dba_objects where 1=0;
insert into test select * from dba_objects; insert/*+ append */into test select * from dba_objects;
在Noarchivelog模式下,对于常规表的Direct insert append只产生少量redo
create table test nologging as select * from dba_objects where 1=0; insert into test select * from dba_objects; insert/*+ append */into test select * from dba_objects;
在Noarchivelog模式下,对于nologging表的Direct insert append也只产生少量redo
b).在归档模式下:
create table test as select * from dba_objects where 1=0; insert into test select * from dba_objects; insert/*+ append */into test select * from dba_objects;
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
create table test nologging as select * from dba_objects where 1=0; insert into test select * from dba_objects; insert/*+ append */into test select * from dba_objects;
在archivelog模式下,对于nologging表的Direct insert append只产生少量redo，
在这种情况下等价于在Noarchivelog模式下Direct insert append
参考信息：http://www.itpub.net/showthread.php?s=&postid=1618916
14）关于nologging，direct insert，UNDO三者之间的关系，biti_rainy有过这样的解释
不管表是否在nologging 下，只要是 direct insert，就不会对数据内容生成undo，也就是不会为insert而记录 rowid
在 direct insert 后回滚数据，实际上并没有进行数据的 删除操作
而是仅仅对空间进行了回收。若是删除，不可能只产生这么少的 redo，这里从另一个侧面证明
即使 logging 下的 direct insert 对于回滚信息，也是不会对数据产生 undo 而仅仅产生空间变化的 undo
参考信息http://www.itpub.net/showthread.php?threadid=217094
小结:
Nologging模式可以使用的操作
1． CTAS创建表
2． Index的创建和重建
3． Insert /*+ append */ into test select—直接路径插入
4． Alter Table操作，如remove,split
更多信息http://search.itpub.net/search.php?s=5ee7a3ad7109a32ae7033f52d68be149&action=showresults&searchid=399212&sortby=lastpost&sortorder=descending
另外在自己测试时可能觉得需要把buffer cache清空一下，可以参考
http://www.eygle.com/archives/2005/12/oracle_howto_flush_buffer_cache.html