行链接消除测试

上次博文测试了行迁移的产生以及如何消除，这次我们再来测试一下行链接的产生以及如何消除。
通常，产生行链接是因为当一行数据大于一个数据块，则ORACLE会同时分配两个数据块，并在第一个块上登记第二个块的地址，从而形成行链接。


[oracle@ora10g ~]$ sqlplus / as sysdba


SQL*Plus: Release 10.2.0.1.0 - Production on 星期二 10月 27 14:11:44 2015


Copyright (c) 1982, 2005, Oracle.  All rights reserved.


Connected to an idle instance.


SYS@ora10g> startup
ORACLE instance started.


Total System Global Area  524288000 bytes
Fixed Size    1220384 bytes
Variable Size  331350240 bytes
Database Buffers  188743680 bytes
Redo Buffers    2973696 bytes
Database mounted.
Database opened.
SYS@ora10g> conn zlm/zlm
Connected.


--创建测试表EMPLOYEES及其索引
ZLM@ora10g> DROP TABLE EMPLOYEES PURGE;


Table dropped.


ZLM@ora10g> CREATE TABLE EMPLOYEES AS SELECT * FROM HR.EMPLOYEES ;


Table created.


ZLM@ora10g> desc EMPLOYEES;
 Name   Null?    Type
 ----------------------------------------- -------- ----------------------------
 EMPLOYEE_ID    NUMBER(6)
 FIRST_NAME    VARCHAR2(20)
 LAST_NAME   NOT NULL VARCHAR2(25)
 EMAIL   NOT NULL VARCHAR2(25)
 PHONE_NUMBER    VARCHAR2(20)
 HIRE_DATE   NOT NULL DATE
 JOB_ID   NOT NULL VARCHAR2(10)
 SALARY    NUMBER(8,2)
 COMMISSION_PCT    NUMBER(2,2)
 MANAGER_ID    NUMBER(6)
 DEPARTMENT_ID    NUMBER(4)


ZLM@ora10g> create index idx_emp_id on employees(employee_id);


Index created.


--修改表结构扩大字段
ZLM@ora10g> alter table EMPLOYEES modify FIRST_NAME VARCHAR2(2000);


Table altered.


ZLM@ora10g> alter table EMPLOYEES modify LAST_NAME  VARCHAR2(2000);


Table altered.


ZLM@ora10g> alter table EMPLOYEES modify EMAIL VARCHAR2(2000);


Table altered.


ZLM@ora10g> alter table EMPLOYEES modify PHONE_NUMBER  VARCHAR2(2000);


Table altered.


--填充相关字段（使其产生行链接）
ZLM@ora10g> UPDATE EMPLOYEES
  SET FIRST_NAME = LPAD('1', 2000, '*'), LAST_NAME = LPAD('1', 2000, '*'), EMAIL = LPAD('1', 2000, '*'),
  PHONE_NUMBER = LPAD('1', 2000, '*');


107 rows updated.


ZLM@ora10g> COMMIT;


Commit complete.


--创建chaind_rows表来观察行链接
ZLM@ora10g> set autotrace off 
ZLM@ora10g> drop table chained_rows purge;


Table dropped.


ZLM@ora10g> @?/rdbms/admin/utlchain.sql


Table created.


ZLM@ora10g> analyze table EMPLOYEES list chained rows into chained_rows;


Table analyzed.


ZLM@ora10g> select count(*)  from chained_rows where table_name='EMPLOYEES';


  COUNT(*)
----------
       107


此时可以看到，这107行数据都产生了行链接。
   
--尝试使用消除行迁移的方法来消除行链接   
ZLM@ora10g> drop table EMPLOYEES_TMP;


Table dropped.


ZLM@ora10g> create table EMPLOYEES_TMP as select * from EMPLOYEES where rowid in (select head_rowid from chained_rows);


Table created.


ZLM@ora10g> Delete from EMPLOYEES where rowid in (select head_rowid from chained_rows);


107 rows deleted.


ZLM@ora10g> Insert into EMPLOYEES select * from EMPLOYEES_TMP;


107 rows created.


ZLM@ora10g> delete from chained_rows ;


107 rows deleted.


ZLM@ora10g> commit;


Commit complete.


ZLM@ora10g> analyze table EMPLOYEES list chained rows into chained_rows;


Table analyzed.


ZLM@ora10g> select count(*)  from chained_rows where table_name='EMPLOYEES';


  COUNT(*)
----------
       107


与消除行迁移不同，使用以上的方法，仍然无法来去除行链接，再重新插入数据后，这107行数据仍然产生了行链接。  
  
ZLM@ora10g> select file_name from dba_data_files;


FILE_NAME
-----------------------------------------------
/u01/app/oracle/oradata/ora10g/undotbs01.dbf
/u01/app/oracle/oradata/ora10g/zlm01.dbf
/u01/app/oracle/oradata/ora10g/example01.dbf
/u01/app/oracle/oradata/ora10g/users01.dbf
/u01/app/oracle/oradata/ora10g/sysaux01.dbf
/u01/app/oracle/oradata/ora10g/system01.dbf


6 rows selected.


create tablespace TBS_32k 
blocksize 32K
datafile  '/u01/app/oracle/oradata/ora10g/TBS_32K.DBF' size 100M  
autoextend on next 10M 
extent management local 
  6  segment space management auto;
create tablespace TBS_32k
*
ERROR at line 1:
ORA-00382: 32768 not a valid block size, valid range [2048..16384]


ORA-00382提示我的10g版本不支持32k的block size，只允许2k..16k之间的大小。


create tablespace TBS_16k 
blocksize 16k
datafile  '/u01/app/oracle/oradata/ora10g/TBS_16K.DBF' size 100M  
autoextend on next 10M 
extent management local 
  6  segment space management auto;
create tablespace TBS_16k
*
ERROR at line 1:
ORA-29339: tablespace block size 16384 does not match configured block sizes


由于没有配置db_nk_block_size参数，因此不允许创建非标准block size的表空间。


ZLM@ora10g> show parameter cache_size


NAME     TYPE VALUE
------------------------------------ ----------- ------------------------------
db_16k_cache_size     big integer 0
db_2k_cache_size     big integer 0
db_32k_cache_size     big integer 0
db_4k_cache_size     big integer 0
db_8k_cache_size     big integer 0
db_cache_size     big integer 0
db_keep_cache_size     big integer 0
db_recycle_cache_size     big integer 0
ZLM@ora10g> alter system set db_16k_cache_size=1m scope=both;


System altered.


ZLM@ora10g> show parameter cache_size


NAME     TYPE VALUE
------------------------------------ ----------- ------------------------------
db_16k_cache_size     big integer 4M
db_2k_cache_size     big integer 0
db_32k_cache_size     big integer 0
db_4k_cache_size     big integer 0
db_8k_cache_size     big integer 0
db_cache_size     big integer 0
db_keep_cache_size     big integer 0
db_recycle_cache_size big integer 0


尽管只分配了1M给db_16k_block_size参数，但默认还是分配了4M，这个和oracle的granule有关，此处不详述。


--创建16k块大小的非标表空间TBS_16k 
ZLM@ora10g> create tablespace TBS_16k 
blocksize 16k
datafile  '/u01/app/oracle/oradata/ora10g/TBS_16K.DBF' size 100M  
autoextend on next 10M 
extent management local 
  6  segment space management auto;


Tablespace created.


ZLM@ora10g> DROP TABLE EMPLOYEES_BK PURGE;
DROP TABLE EMPLOYEES_BK PURGE
           *
ERROR at line 1:
ORA-00942: table or view does not exist



--创建基于16k块大小的表空间重新创建测试表EMPLOYEES_BK
ZLM@ora10g> CREATE TABLE EMPLOYEES_BK TABLESPACE TBS_16K AS SELECT * FROM EMPLOYEES;


Table created.


ZLM@ora10g> delete from chained_rows ;


107 rows deleted.


ZLM@ora10g> commit;


Commit complete.


ZLM@ora10g> analyze table EMPLOYEES_BK list chained rows into chained_rows;


Table analyzed.


ZLM@ora10g> select count(*)  from chained_rows where table_name='EMPLOYEES_BK';


  COUNT(*)
----------
0

此时看到chained_rows表的记录为0，说明没有产生行链接了。因此，只有通过增加block size的大小，才能真正消除行迁移。