在Oracle中，有些表由于頻繁的插入和刪除數據，導致高水位過高，表的碎片也很高，如何判斷呢？

drop table test purge;

      6.59     33M         80.02%  

--把表收縮一下，碎片率下降了

alter table test enable row movement;alter table test shrink space;select trunc(real_size('TEST')/1024/1024, 2) real_size,       bytes /1024/1024||'M' seg_size,       trunc((1 - real_size('TEST')/ bytes) * 100, 2) || '%' frag_ratio  from user_segments s where s.segment_name='TEST'; REAL_SIZE SEG_SIZE    FRAG_RATIO---------- ----------- -------------     3.2     3.25M      1.53%

附錄是Tom kyte提供的檢查腳本：

CREATE OR REPLACE FUNCTION REAL_SIZE(P_SEGNAME IN VARCHAR2,P_OWNER IN VARCHAR2 DEFAULT USER,P_TYPE IN VARCHAR2 DEFAULT 'TABLE')RETURN NUMBER AUTHID CURRENT_USER ASL_TOTAL_BLOCKS NUMBER;L_TOTAL_BYTES NUMBER;L_UNUSED_BLOCKS NUMBER;L_UNUSED_BYTES NUMBER;L_LASTUSEDEXTFILEID NUMBER;L_LASTUSEDEXTBLOCKID NUMBER;L_LAST_USED_BLOCK NUMBER;L_UNFORMATTED_BLOCKS NUMBER;L_UNFORMATTED_BYTES NUMBER;L_FS1_BLOCKS NUMBER;L_FS1_BYTES NUMBER;L_FS2_BLOCKS NUMBER;L_FS2_BYTES NUMBER;L_FS3_BLOCKS NUMBER;L_FS3_BYTES NUMBER;L_FS4_BLOCKS NUMBER;L_FS4_BYTES NUMBER;L_FULL_BLOCKS NUMBER;L_FULL_BYTES NUMBER;T_TOTAL_BYTES NUMBER;T_FS_BYTES NUMBER;P_PART_NAME VARCHAR2(30);BEGINDBMS_SPACE.SPACE_USAGE(P_OWNER,P_SEGNAME,P_TYPE,L_UNFORMATTED_BLOCKS,L_UNFORMATTED_BYTES,L_FS1_BLOCKS,L_FS1_BYTES,L_FS2_BLOCKS,L_FS2_BYTES,L_FS3_BLOCKS,L_FS3_BYTES,L_FS4_BLOCKS,L_FS4_BYTES,L_FULL_BLOCKS,L_FULL_BYTES,P_PART_NAME);DBMS_SPACE.UNUSED_SPACE(P_OWNER,P_SEGNAME,P_TYPE,L_TOTAL_BLOCKS,L_TOTAL_BYTES,L_UNUSED_BLOCKS,L_UNUSED_BYTES,L_LASTUSEDEXTFILEID,L_LASTUSEDEXTBLOCKID,L_LAST_USED_BLOCK,P_PART_NAME);T_FS_BYTES := L_FS1_BYTES * 0.25 / 2 + L_FS2_BYTES * (0.5 + 0.25) / 2 +L_FS3_BYTES * (0.75 + 0.5) / 2 +L_FS4_BYTES * (1 + 0.75) / 2 + L_UNUSED_BYTES;T_TOTAL_BYTES := L_TOTAL_BYTES;RETURN T_TOTAL_BYTES-T_FS_BYTES;EXCEPTIONWHEN OTHERS THENRETURN 1;END;