降低HWM，消除行移植和行链接。

我们可以用下面的办法来最方便的进行重组，消除row migration：

SQL> alter table t add t1 date default sysdate;

Table altered.

SQL> c/t1/t2
1* alter table t add t2 date default sysdate
SQL> /

Table altered.

SQL> c/t2/t3
1* alter table t add t3 date default sysdate
SQL> /

Table altered.

SQL> analyze table t compute statistics;

Table analyzed.

SQL> select table_name,num_rows,CHAIN_CNT from user_tables where table_name='T';

TABLE_NAME NUM_ROWS CHAIN_CNT
------------------------------ ---------- ----------
T 41616 3908

SQL> alter table t move ;

Table altered.

SQL> analyze table t compute statistics;

Table analyzed.

SQL> select table_name,num_rows,CHAIN_CNT from user_tables where table_name='T';

TABLE_NAME NUM_ROWS CHAIN_CNT
------------------------------ ---------- ----------
T 41616 0

Index 需要rebuild 或者删除重建 。

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如何消除表中的chained rows?（测试表中存在较多的链接行）
创建chained rows需要的表：
sql> @/home/oracle/product/9.2.0/rdbms/admin/utlchain.sql
将表中的chained row移动到chained_rows表
sql> analyze table test_table_name list chained rows;
sql> select table_name,head_rowid from chained_rows
where table_name = ‘TEST_TABLE_NAME’;
sql> select * from agent_account where rowid in
(select head_rowid from chained_rows where table_name = ‘TEST_TABLE_NAME’)

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