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 4 124 43

SQL> alter system dump datafile 4 block 124;

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

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