oracle表优化方法教程

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1、建立实验表

create table t_pctfree

    (

    id number,

    name varchar2(2000),

    name1 varchar2(2000),

    name2 varchar2(2000),

    name3 varchar2(2000),

    name4 varchar2(2000)

    )

   tablespace users

   pctfree 10;

Table created.

2、添加数据，先只写id，其他值为null

SQL>insert into t_pctfree(id) values(2);

1 row created.

SQL> commit;

Commit complete.

3、使用dump查看数据块，确定id为2的数据只存在于一个块中

SQL> select dbms_rowid.rowid_block_number(rowid) block_id from t_pctfree where id=2;

  BLOCK_ID

----------

     47547

SQL> alter system dump datafile 5 block 51031;

System altered.

SQL> oradebug setmypid;

Statement processed.

SQL> oradebug tracefile_name;

/u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_26496.trc

[oracle@localhost trace]$ more /u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_26496.trc

tab 0, row 0, @0x1f92

tl: 2 fb: --HDFL-- lb: 0x2 

tab 0, row 1, @0x1f8c

tl: 6 fb: --H-FL-- lb: 0x0  cc: 1

col  0: [ 2]  c1 03

tab 0, row 2, @0x1f86

SQL> var n number;

SQL> exec dbms_stats.convert_raw_value('c103',:n);

PL/SQL procedure successfully completed.

SQL> print :n

N

----------

2

4、修改id为2的数据，使当前块剩余空间容纳不下修改后的数据

SQL> update scott.t_pctfree set name=dbms_random.string('u', 2000) where id=2;

1 row updated.

SQL> commit;

Commit complete.

SQL> alter system switch logfile;

System altered.

SQL> /

System altered.

SQL> /

System altered.

.

5、查看修改后的块状态

SQL> select dbms_rowid.rowid_block_number(rowid) block_id from t_pctfree where id=2;

  BLOCK_ID

----------

     47547

SQL> alter system dump datafile 5 block 51031;

System altered.

SQL> oradebug setmypid;

Statement processed.

SQL> oradebug tracefile_name;

/u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_26496.trc

[oracle@localhost trace]$ more /u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_26496.trc

tab 0, row 1, @0xdec

tl: 9 fb: --H----- lb: 0x1  cc: 0

nrid:  0x0140c75b.0

6、发现已产生行迁移，源块只留下了迁移块的地址，通过nrid查看迁移目标块信息

SQL> select dbms_utility.DATA_BLOCK_ADDRESS_FILE(to_number('0140c75b', 'xxxxxxxxxx')) file#,dbms_utility.DATA_BLOCK_ADDRESS_BLOCK(to_number('0140c75b','xxxxxxxxxx')) block# from dual;

     FILE#     BLOCK#

---------- ----------

551035

SQL> alter system dump datafile 5 block 51035;

System altered.

SQL> oradebug setmypid;

Statement processed.

SQL> oradebug tracefile_name;

/u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_26496.trc

[oracle@localhost trace]$ more /u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_26496.trc

tab 0, row 0, @0x17a1

tl: 2015 fb: ----FL-- lb: 0x1  cc: 2

hrid: 0x0140b9bb.1

col  0: [ 2]  c1 03

col  1: [2000]

 5a 52 57 58 53 54 45 4a 50 4e 56 43 4c 55 4e 4e 4d 47 59 49 51 50 44 41 41

 4b 4d 47 56 52 49 5a 51 55 47 54 54 5a 51 41 49 5a 55 57 43 58 46 42 54 55

7、可以看到迁移目标块只有hrid，没有nrid，说明只出现了行迁移，没有出现行链接

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