在Oracle 11g以前,如果要在一个大表中增加一列,并设置默认值,那将是一个非常悲剧的事情.有些时候不得不选择在线重定义功能来实现
oracle 11g增加列,并带默认值的新特性
[日期：2014-04-05] 来源：Linux社区 作者：Linux [字体：]
在Oracle 11g以前,如果要在一个大表中增加一列,并设置默认值,那将是一个非常悲剧的事情.有些时候不得不选择在线重定义功能来实现该需求.而在11g中增加新列并设置默认值,只是简单的修改数据字典来实现该功能,大大提供效率
10g加列(默认值)
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for Linux: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
SQL> create table t_xifenfei
2 as select object_id,object_name from dba_objects;
Table created.
SQL> select count(*) from t_xifenfei;
COUNT(*)
----------
49827
SQL> desc t_xifenfei
Name Null? Type
----------------------------------------- -------- ----------------------------
OBJECT_ID NUMBER
OBJECT_NAME VARCHAR2(128)
SQL> set timing on
SQL> alter table t_xifenfei add c_xff varchar2(100) default 'www.xifenfei.com' not null;
Table altered.
Elapsed: 00:00:06.13
--使用了6秒钟
SQL> select rowid,
2 dbms_rowid.rowid_relative_fno(rowid)rel_fno,
3 dbms_rowid.rowid_block_number(rowid)blockno,
4 dbms_rowid.rowid_row_number(rowid) rowno
5 from t_xifenfei where object_name='OBJ$';
ROWID REL_FNO BLOCKNO ROWNO
------------------ ---------- ---------- ----------
AAAMwJAAEAAAAB8AAr 4 124124 43
SQL> alter system dump datafile 4 block 124124;
System altered.
Elapsed: 00:00:00.08
11g增加列(默认值)
SQL> select * from v$version;
BANNER
-----------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
PL/SQL Release 11.2.0.3.0 - Production
CORE 11.2.0.3.0 Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
SQL> create table t_xifenfei
2 as select object_id,object_name from dba_objects;
Table created.
SQL> select count(*) from t_xifenfei;
COUNT(*)
----------
74605
SQL> select rowid,
2 dbms_rowid.rowid_relative_fno(rowid)rel_fno,
3 dbms_rowid.rowid_block_number(rowid)blockno,
4 dbms_rowid.rowid_row_number(rowid) rowno
5 from t_xifenfei where object_name='OBJ$';
ROWID REL_FNO BLOCKNO ROWNO
------------------ ---------- ---------- ----------
AAASpRAAEAAAACrAAu 4 171 46
SQL> alter system dump datafile 4 block 171;
System altered.
SQL> set timing on
SQL> alter table t_xifenfei add c_xff varchar2(100) default 'www.xifenfei.com' not null;
Table altered.
Elapsed: 00:00:00.19
--只是使用了0.19秒
SQL> select rowid,
2 dbms_rowid.rowid_relative_fno(rowid)rel_fno,
3 dbms_rowid.rowid_block_number(rowid)blockno,
4 dbms_rowid.rowid_row_number(rowid) rowno
5 from t_xifenfei where object_name='OBJ$';
ROWID REL_FNO BLOCKNO ROWNO
------------------ ---------- ---------- ----------
AAASpRAAEAAAACrAAu 4 171 46
Elapsed: 00:00:00.04
SQL> alter system dump datafile 4 block 171;
System altered.
通过10g和11g的增加相同列和默认值的对比可以发现,11g的速度要比10g快很多很多,下面我们通过上面dump出来相关的数据块来分析原因
dump分析
11g增加列之前dump
tab 0, row 0, @0x1f74
tl: 12 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [ 2] c1 15
col 1: [ 5] 49 43 4f 4c 24
tab 0, row 1, @0x1f66
tl: 14 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [ 2] c1 2f
col 1: [ 7] 49 5f 55 53 45 52 31
tab 0, row 2, @0x1f5b
tl: 11 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [ 2] c1 1d
col 1: [ 4] 43 4f 4e 24
11g增加列之后dump
tab 0, row 0, @0x1f74
tl: 12 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [ 2] c1 15
col 1: [ 5] 49 43 4f 4c 24
tab 0, row 1, @0x1f66
tl: 14 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [ 2] c1 2f
col 1: [ 7] 49 5f 55 53 45 52 31
tab 0, row 2, @0x1f5b
tl: 11 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [ 2] c1 1d
col 1: [ 4] 43 4f 4e 24
tab 0, row 3, @0x1f4f
tl: 12 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [ 2] c1 10
col 1: [ 5] 55 4e 44 4f 24
10g增加列之后dump
因为10g在没有增加列之前的dump和11g未增加列之前类似,所以未dump出来
tab 0, row 0, @0x1f63
tl: 29 fb: --H-FL-- lb: 0x2 cc: 3
col 0: [ 2] c1 15
col 1: [ 5] 49 43 4f 4c 24
col 2: [16] 77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 1, @0x1f44
tl: 31 fb: --H-FL-- lb: 0x2 cc: 3
col 0: [ 2] c1 2d
col 1: [ 7] 49 5f 55 53 45 52 31
col 2: [16] 77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 2, @0x1f28
tl: 28 fb: --H-FL-- lb: 0x2 cc: 3
col 0: [ 2] c1 1d
col 1: [ 4] 43 4f 4e 24
col 2: [16] 77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 3, @0x1f0b
tl: 29 fb: --H-FL-- lb: 0x2 cc: 3
col 0: [ 2] c1 10
col 1: [ 5] 55 4e 44 4f 24
col 2: [16] 77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
