如何检查oracle表或索引可回收空间
如何检查oracle表或索引可回收空间
发布时间:2015-06-05 来源:查字典编辑
摘要:对表进行大量删除后,可能会有很多空闲空间可以回收,相关计算方法参考如下:更新统计信息Analyzetablecomputestatistic...

对表进行大量删除后,可能会有很多空闲空间可以回收,相关计算方法参考如下:

更新统计信息

Analyze table compute statistics ;

计算碎片空间

SELECT TABLE_NAME , (BLOCKS *8192 / 1024/1024 ) - (NUM_ROWS*AVG_ROW_LEN/1024/1024)

"Data lower than HWM in MB" FROM DBA_TABLES WHERE UPPER(owner) =UPPER('&OWNER') order by 2 desc;

ANALYZE TABLE big_emp1 ESTIMATE STATISTICS;

SELECT table_name,num_rows,blocks,empty_blocks

FROM user_tables

WHERE table_name='BIG_EMP1';

SELECT COUNT (DISTINCT

DBMS_ROWID.ROWID_BLOCK_NUMBER(rowid)||

DBMS_ROWID.ROWID_RELATIVE_FNO(rowid)) "Used"

FROM big_emp1;

SELECT segment_name,segment_type,blocks

FROM dba_segments

WHERE segment_name='BIG_EMP1';

对于索引

校验结构

analyze index validate structure;

检查

column name format a15

column blocks heading "ALLOCATED|BLOCKS"

column lf_blks heading "LEAF|BLOCKS"

column br_blks heading "BRANCH|BLOCKS"

column Empty heading "UNUSED|BLOCKS"

select name,

blocks,

lf_blks,

br_blks,

blocks-(lf_blks+br_blks) empty

from index_stats;

或者

select name, btree_space, used_space, pct_used from index_stats;

回收空间方法

'Compatible' 必须 >=10.0

1. Enable row movement for the table.

SQL> ALTER TABLE scott.emp ENABLE ROW MOVEMENT;

2. Shrink table but don't want to shrink HWM (High Water Mark).

SQL> ALTER TABLE scott.emp SHRINK SPACE COMPACT;

3. Shrink table and HWM too.

SQL> ALTER TABLE scott.emp SHRINK SPACE;

4. Shrink table and all dependent index too.

SQL> ALTER TABLE scott.emp SHRINK SPACE CASCADE;

5. Shrink table under MView.

SQL> ALTER TABLE

SHRINK SPACE;

6. Shrink Index only.

SQL> ALTER INDEX SHRINK SPACE;

验证

SQL> set serveroutput on

SQL> declare

2 v_unformatted_blocks number;

3 v_unformatted_bytes number;

4 v_fs1_blocks number;

5 v_fs1_bytes number;

6 v_fs2_blocks number;

7 v_fs2_bytes number;

8 v_fs3_blocks number;

9 v_fs3_bytes number;

10 v_fs4_blocks number;

11 v_fs4_bytes number;

12 v_full_blocks number;

13 v_full_bytes number;

14 begin

15 dbms_space.space_usage ('SYSTEM', 'T_SHRINK', 'TABLE', v_unformatted_blocks,

16 v_unformatted_bytes, v_fs1_blocks, v_fs1_bytes, v_fs2_blocks, v_fs2_bytes,

17 v_fs3_blocks, v_fs3_bytes, v_fs4_blocks, v_fs4_bytes, v_full_blocks, v_full_bytes);

18 dbms_output.put_line('Unformatted Blocks = '||v_unformatted_blocks);

19 dbms_output.put_line('FS1 Blocks = '||v_fs1_blocks);

20 dbms_output.put_line('FS2 Blocks = '||v_fs2_blocks);

21 dbms_output.put_line('FS3 Blocks = '||v_fs3_blocks);

22 dbms_output.put_line('FS4 Blocks = '||v_fs4_blocks);

23 dbms_output.put_line('Full Blocks = '||v_full_blocks);

24 end;

25 /

Unformatted Blocks = 0

FS1 Blocks = 0

FS2 Blocks = 0

FS3 Blocks = 0

FS4 Blocks = 2

Full Blocks = 1

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