诊断行迁移，行链接，及解决方法

获取row chain and row Migration

1.使用analyze对相应的object分析
SQL> ANALYZE TABLE oe.orders COMPUTE STATISTICS;
Table Analyzed.

SQL> SELECT num_rows, avg_row_len, chain_cnt
2 FROM DBA_TABLES
3 WHERE table_name='ORDERS';
NUM_ROWS AVG_ROW_LEN CHAIN_CNT
---------- ----------- ----------
1171 67 83

2.也可是使用以下方法获取Migrated Rows：

ANALYZE TABLE … LIST CHAINED ROWS ------不会覆盖当前统计信息
在使用以上命令时需要执行utlchain.sql这个脚本，也可以手工执行：

SQL> CREATE TABLE chained_rows (
2 owner_name VARCHAR2(30),
3 table_name VARCHAR2(30),
4 cluster_name VARCHAR2(30),
5 partition_name VARCHAR2(30),
6 head_rowid ROWID,
7 analyze_timestamp DATE );

用于存储链接行的信息

eg：

SQL> ANALYZE TABLE oe.orders LIST CHAINED ROWS;
Table analyzed.

SQL> SELECT owner_name, table_name, head_rowid
2 FROM chained_rows
3 WHERE table_name = 'ORDERS';
OWNER_NAME TABLE_NAME HEAD_ROWID
---------- ---------- ------------------
SALES ORDER_HIST AAAAluAAHAAAAA1AAA
SALES ORDER_HIST AAAAluAAHAAAAA1AAB
...

消除行迁移：
? Export/import:
Export the table.
Drop or truncate the table.
Import the table.

? MOVE table command:
ALTER TABLE EMPLOYEES MOVE
所有index在操作后需要rebuilt
Move table command is faster than export and impor t.
但是前提是有足够的空间。

? Online table redefinition
使用 DBMS_REDEFINITION 包需要足够空间。

? Copy migrated rows:
Find migrated rows by using ANALYZE.
Copy migrated rows to a new table.
Delete migrated rows from the original table.
Copy rows from the new table to the original table.

注意，是否需要禁用相应的外键约束，trigger ，row-level security, and auditing.

script：

/* Clean up from last execution */
SET ECHO OFF
DROP TABLE migrated_rows;
DROP TABLE chained_rows;

/* Create the CHAINED_ROWS table */
@?/rdbms/admin/utlchain
SET ECHO ON
SPOOL fix_mig

/* List the chained & migrated rows */
ANALYZE TABLE &table_name LIST CHAINED ROWS;

/* Copy the chained/migrated rows to another table */
CREATE TABLE migrated_rows AS
SELECT orig.*
FROM &table_name orig, chained_rows cr
WHERE orig.rowid = cr.head_rowid
AND cr.table_name = upper('&table_name');

/* Delete the chained/migrated rows from the original table */
DELETE FROM &table_name
WHERE rowid IN (
SELECT head_rowid
FROM chained_rows);

/* Copy the chained/migrated rows back into the original table */
INSERT INTO &table_name
SELECT *
FROM migrated_rows;
SPOOL OFF