第一種情況
(非歸檔模式下)創建表T01:
SQL> create table t01 as select * from dba_objects where 1=2;
Table created.
(非歸檔模式下)查看當前redo大小:
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size'
5 /
VALUE
----------
49784
(非歸檔模式下)普通INSERT語句插入:
SQL> insert into t01 select * from dba_objects;
11698 rows created.
(非歸檔模式下)查看普通INSERT語句執行後,當前redo大小:
SQL> select value
from v$mystat,v$statname
2 3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size';
VALUE
----------
1305724
(非歸檔模式)採用HINT /*+ append*/執行INSERT語句:
SQL> insert /*+ append */ into t01 select * from dba_objects;
11698 rows created.
(非歸檔模式)查詢帶/*+ append*/的INSERT執行後,當前redo大小:
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size';
VALUE
----------
1308140
(非歸檔模式)計算使用HINT(/*+ append*/)和普通INSERT語句分別產生的redo大小:
SQL> select (1308140-1305724) redo_append,(1305724-49784) redo from dual;
REDO_APPEND REDO
----------- ----------
2416 1255940
可見,在非歸檔模式下,INSERT語句採用HINT /*+ APPEND*/的方式確實比普通INSERT語句產生的redo要少很多。
第二種情況
下面測試歸檔模式下
SQL> archive log list
Database log mode Archive Mode
Automatic archival Enabled
Archive destination /u01/arch
Oldest online log sequence 109
Next log sequence to archive 111
Current log sequence 111
(歸檔模式)查看當前redo大小:
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size'
5 /
VALUE
----------
19540
(歸檔模式)執行普通INSERT語句:
SQL> insert into t01 select * from dba_objects;
11698 rows created.
(歸檔模式)普通INSERT方式產生的redo大小:
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size'
5 /
VALUE
----------
1218884
(歸檔模式)採用HINT /*+ append*/執行INSERT語句:
SQL> insert /*+ append */ into t01 select * from dba_objects;
11698 rows created.
(歸檔模式)查詢帶/*+ append*/的INSERT執行後,當前redo大小:
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size';
VALUE
----------
2451664
(歸檔模式)計算使用HINT(/*+ append*/)和普通INSERT語句分別產生的redo大小:
SQL> select (2451664-1218884) redo_append,(1218884-19540) from dual;
REDO_APPEND (1218884-19540)
----------- ---------------
1232780 1199344
可見,在歸檔模式下,採用HINT與普通INSERT方式產生的redo量是相當的,且略大於普通INSERT語句產生的redo量。
第三種情況
再看一種情況,歸檔模式,T01也是LOGGING模式
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size'
5 /
VALUE
----------
2541780
SQL> insert /*+ append nologging */ into t01 select * from dba_objects;
或者執行:
SQL> insert /*+ append */ into t01 nologging select * from dba_objects;
也將產生redo的量爲:1233040。
=========================================
第四種情況
(歸檔模式)修改T01的屬性爲NOLOGGING:
SQL> alter table t01 nologging;
Table altered.
SQL> select table_name,logging from dba_tables where table_name='T01';
TABLE_NAME LOG
------------------------------ ---
T01 NO
(歸檔模式)查看當前redo值:
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size'
5 /
VALUE
----------
5010600
(歸檔模式)執行普通INSERT語句:
SQL> insert into t01 select * from dba_objects;
11698 rows created.
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size'
5 /
VALUE
----------
6209848
(歸檔模式)採用HINT /*+ append*/執行INSERT語句:
SQL> insert /*+ append */ into t01 select * from dba_objects;
11698 rows created.
SQL> select value
2 from v$mystat,v$statname
3 where v$mystat.statistic#=v$statname.statistic#
4 and v$statname.name='redo size'
5 /
VALUE
----------
6210536
(歸檔模式)計算兩者產生的redo差值:
SQL> select (6210536-6209848) redo_append,(6209848-5010600) redo from dual;
REDO_APPEND REDO
----------- ----------
688 1199248
可見,在歸檔模式下,將表調整爲NOLOGGING,產生的redo量是最少的!
對比一下:
非歸檔,T01(LOGGING),普通INSERT語句產生的redo值:1255940
非歸檔,T01(LOGGING),HINT /*+append*/,產生的redo值:2416
歸檔,T01(LOGGING),普通INSERT語句產生的redo值:1199344
歸檔,T01(LOGGING),HINT /*+ append*/,產生的redo值:1232780
歸檔,T01(LOGGING),/*+append*/ + nologging,產生的redo值:1233040
歸檔,T01(NOLOGGING),普通INSERT語句產生的redo值:688
歸檔,T01(NOLOGGING),HINT /*+append*/,產生的redo值:1199248
綜合以上的數據,可以明白,如果想INSERT語句執行的更快,產生更少的redo,分兩種情況:
非歸檔模式:在INSERT語句中使用HINT /*+ append */
歸檔模式:將目標表修改爲NOLOGGING(alter table xxx nologging),然後在INSERT語句中使用HINT /*+ append */(建議完成後做一次數據庫備份)