在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$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for Linux: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
SQL> create table t_xifenfei
2 as select object_id,object_name from dba_objects;
Table created.
SQL> select count(*) from t_xifenfei;
COUNT(*)
----------
49827
SQL> desc t_xifenfei
Name Null? Type
----------------------------------------- -------- ----------------------------
OBJECT_ID NUMBER
OBJECT_NAME VARCHAR2(128)
SQL> set timing on
SQL> alter table t_xifenfei add c_xff varchar2(100) default 'www.orasos.com' not null;
Table altered.
Elapsed: 00:00:06.13
--使用了6秒钟
SQL> select rowid,
2 dbms_rowid.rowid_relative_fno(rowid)rel_fno,
3 dbms_rowid.rowid_block_number(rowid)blockno,
4 dbms_rowid.rowid_row_number(rowid) rowno
5 from t_xifenfei where object_name='OBJ$';
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.orasos.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
对比发现11g在增加列之后,以前的数据dump出来的内容未有任何改变.也就是说:在10g中,我们增加一个列和默认值,会自动的增加到真实的数据中,而在11g中增加列和默认值并未真的加到11g的表中已经存在的数据中.
11g中插入新数据dump测试
SQL> insert into chf.t_xifenfei(object_id,object_name) 2 select object_id,object_name FROM DBA_OBJECTS; 74605 rows created. SQL> commit; Commit complete. SQL> ALTER SYSTEM FLUSH BUFFER_CACHE; System altered. SQL> / System altered. --建议刷新 SQL> SQL> 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 chf.t_xifenfei where object_name='OBJ$'; ROWID REL_FNO BLOCKNO ROWNO ------------------ ---------- ---------- ---------- AAASpRAAEAAAACrAAu 4 171 46 AAASpRAAEAAAB5TAAu 4 7763 46 SQL> ALTER SYSTEM DUMP DATAFILE 4 BLOCK 7763; System altered. --dump内容 tab 0, row 0, @0x4e3 tl: 29 fb: --H-FL-- lb: 0x1 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, @0x500 tl: 31 fb: --H-FL-- lb: 0x1 cc: 3 col 0: [ 2] c1 2f 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, @0x51f tl: 28 fb: --H-FL-- lb: 0x1 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, @0x53b tl: 29 fb: --H-FL-- lb: 0x1 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
通过这里看看出:在11g中后续插入的数据,默认值也插入到数据文件中
