oracle优化--表优化（行迁移产生实验）-优快云博客

本文通过创建表并填充数据，展示了Oracle数据库中行迁移的过程。首先建立了一个带有多个VARCHAR2字段的表，并设置PCTFREE参数。接着插入一条记录，之后通过更新增大该记录的大小，触发行迁移现象。最后通过系统命令和跟踪文件确认了行迁移的发生。

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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

----------

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#

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

5 51035

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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