获取row chain and row Migration
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
