日志记录模式的转换
a.数据库从非强制日子模式切换到强制日志模式
SQL>alter database force logging;
b.数据库从强制日志模式切换到非强制日志模式
SQL>alter database noforce logging;
c.表空间级别从强制日志模式切换到非强制日志模式
SQL>alter tablespace tablespacename noforce logging;
d.表空间级别从非强制日志模式切换到强制日志模式
SQL>alter tablespace tablespacename force logging;
e.对象级别日志记录模式
SQL>alter tablet mytest nologging; --不记录日志模式
SQL>alter tablet mytest logging; --采用日志记录模式
一、表段，索引段上使用一般DDL，DML时，LOGGING与NOLOGGING情况
1.查看数据库的归档模式
有关设置日志归档模式的问题，请参考：
Oracle 联机重做日志文件(ONLINE LOG FILE)
Oracle 归档日志
SQL> select log_mode,force_logging from v$database;
LOG_MODE FOR
------------ ---
ARCHIVELOG NO
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination /u01/mytest/arch
Oldest online log sequence 1024
Next log sequence to archive 1025
Current log sequence 1025
SQL> select tablespace_name,logging,force_logging from dba_tablespaces;
TABLESPACE_NAME LOGGING FOR
------------------------------ --------- ---
SYSTEM LOGGING NO
UNDOTBS1 LOGGING NO
SYSAUX LOGGING NO
TEMP NOLOGGING NO
USERS LOGGING NO
PERFSTAT LOGGING NO
2.使用如下语句进行查询
SQL >SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';
3.在归档模式下比较表段上的NOLOGGING与LOGGING
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';
NAME VALUE
--------------- ----------
redo size 1644
SQL> CREATE TABLE mytest_nolog NOLOGGING AS SELECT * FROM dba_objects; --nologging模式创建表
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';
NAME VALUE
--------------- ----------
redo size 70064
SQL> select 1644 last,70064 as cur,(70064-1644) diff from dual;--使用nologging模式建表产生的redo size为
LAST CUR DIFF
---------- ---------- ----------
1644 70064 68420
SQL> CREATE TABLE mytest LOGGING AS SELECT * FROM dba_objects; --使用logging模式来创建表
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';; --查看当前的redo size
NAME VALUE
--------------- ----------
redo size 1344112
SQL> select 70064 last,1344112 as cur,(1344112-70064) diff from dual;
LAST CUR DIFF
---------- ---------- ----------
70064 1344112 1274048 ----查看logging模式产生的redo size 为-68420=1274048,比nologging日志模,有19倍多！
SQL> select table_name,logging from user_tables where table_name like 'MYTEST%';--查看创建表的日志记录模式
TABLE_NAME LOG
------------------------------ ---
MYTEST YES
MYTEST_NOLOG NO
4.基于索引来比较redo size(同样是在归档模式下)
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';; --查看当前的redo_size
NAME VALUE
--------------- ----------
redo size 1140
SQL> create index idx_mytest on mytest(object_id); --基于表mytest来创建索引
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';; --查看当前的redo_size
NAME VALUE
--------------- ---------- --基于loggiing模式，创建索引产生的redo size 为221600-1140=220460
redo size 221600
SQL> alter index idx_mytest rebuild; --重建索引
SQL> select 221600 last,448132 cur,448132-221600 diff from dual;
LAST CUR DIFF
---------- ---------- ----------
221600 448132 226532 --重建索引产生的日志比直接建还要多，主要是重建过程还有一个对旧索引的删除
SQL> alter index idx_mytest rebuild nologging; --使用nologging重建索引。
--也可以在创建索引的时候直接使用nologging关键字
--如：create index idx_mytest_nolog mytest_nolog(object_id) nologging
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';; --查看当前的redo size
NAME VALUE
--------------- ---------- --基于nologging日志模式重建索引产生的redo size为469160-448132=21028
redo size 469160
5.非归档模式下的LOGGING与NOLOGGING
SQL> drop table mytest purge;
SQL> drop table mytest_nolog purge;
SQL> select log_mode,force_logging from v$database; --切换日志到非归档模式后，下面是查询的结果
LOG_MODE FOR
------------ ---
NOARCHIVELOG NO
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';; --查看当前的redo size
NAME VALUE
--------------- ----------
redo size 1688
SQL> create table mytest as select * from dba_objects; --创建表对象，使用logging日志记录模式
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';; --查看当前的redo size
NAME VALUE
--------------- ---------- --使用logging日志记录模式，创建表对象之后产生的redo size 为-1688 =68548
redo size 70236
SQL> create table mytest_nolog nologging as select * from dba_objects; --创建表对象，使用nologging日志记录模式
SQL> SELECT a.name,b.value FROM v$statname a JOIN v$mystat b ON a.statistic# = b.statistic# WHERE a.name = 'redo size';; --查看当前的redo size
NAME VALUE
--------------- ---------- --使用nologging日志记录模式创建表对象之后产生的redo size为135464-70236=65228
redo size 135464
6.小结：
使用logging与nologging来创建对象或执行DML时
对于非归档模式下，其产生的日志信息(redo size)相差的并不大
对于归档模式下，logging模式产生的日志将远远大于使用nologging模式产生的日志量