Oracle降低高水位

1.建立測試表
SQL> create table t1 (id int);

Table created.


2.檢視表占用的塊數量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------

3.對T1表做統計資訊收集
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;

Table analyzed.


4.再次檢視表占用的塊數量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------
     0          7      0

5.向表中插入1000W條資料
declare
i number;
begin
for i in 1..10000000 loop
 insert into t1 values(i);
end loop;
commit;
end;
/


6.檢視表占用的塊數量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------
     0          7      0

7.統計資訊收集
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;

Table analyzed.

8.再次檢視表占用的塊數量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------
     15155        204   10000000

9.删除資料
SQL> delete from t1;

10000000 rows deleted.

SQL> commit;

Commit complete.


10.檢視表占用的塊數量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------
     15155        204   10000000

11.統計資訊收集
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;

Table analyzed.


12.再次檢視表占用的塊數量，可以看到
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------
     15155        204      0

13.降低高水位操作
SQL> alter table T1 move;

Table altered.


14.再次檢視表占用的塊數量
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------
     15155        204      0


15.再次收集統計資訊
SQL> ANALYZE TABLE T1 COMPUTE STATISTICS;

Table analyzed.

16.檢視表占用的塊數量，可以看到執行alter table T1 move指令後，高水位已經下降了。
SQL> SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';

    BLOCKS EMPTY_BLOCKS   NUM_ROWS
---------- ------------ ----------
     0          7      0      

ANALYZE TABLE T1 COMPUTE STATISTICS;      分析表
SELECT blocks, empty_blocks, num_rows FROM dba_tables WHERE table_name='T1';   查詢高水位線方法
 1：alter table T1 enable row movement;    開啟行遷移(收縮表操做第一步)
 alter table T1 shrink space ;     收縮表空間
 alter table T1 disable row movement;   關閉行遷移方法 
 2：alter table T1 move;    移動表需要建立索引
 create Index new_index On T1(deptno);   單一索引
 create Index new_index  on T1(deptno,job);   複合索引方法 
 3：truncate table T1;  清空表方法 
 4：create table T1_NEW as select * from T1 where 1=2;
 建立新表alter table T1_NEW rename to T1;    重命名新表