Oracle收缩表空间

可以使用 alter database datafile 'file path...' resize xM 的命令来缩小数据文件。

SELECT 'alter database datafile ''' || A.FILE_NAME || ''' resize ' ||
        ROUND(A.FILESIZE - (A.FILESIZE - C.HWMSIZE - 100) * 0.8) || 'M;',
       A.FILESIZE || 'M' AS "数据文件的总大小", C.HWMSIZE || 'M' AS "数据文件的实用大小"
FROM   (SELECT FILE_ID, FILE_NAME, ROUND(BYTES / 1024 / 1024) AS FILESIZE
         FROM   DBA_DATA_FILES) A,
       (SELECT FILE_ID, ROUND(MAX(BLOCK_ID) * 8 / 1024) AS HWMSIZE
         FROM   DBA_EXTENTS
         GROUP  BY FILE_ID) C
WHERE  A.FILE_ID = C.FILE_ID AND
       A.FILESIZE - C.HWMSIZE > 100;

or

SELECT 'alter database ' || A.NAME || ' datafile ''' || B.FILE_NAME || '''' ||
        ' resize ' ||
        GREATEST(TRUNC(BYTES_FULL / .7), (BYTES_TOTAL - BYTES_FREE)) ||
        CHR(10) || '--tablespace was ' ||
        TRUNC(BYTES_FULL * 100 / BYTES_TOTAL) || '% full now ' ||
        TRUNC(BYTES_FULL * 100 /
              GREATEST(TRUNC(BYTES_FULL / .7), (BYTES_TOTAL - BYTES_FREE))) || '%'
FROM   V$DATABASE A, DBA_DATA_FILES B,
       (SELECT TABLESPACE_NAME, SUM(BYTES) BYTES_FULL
         FROM   DBA_EXTENTS
         GROUP  BY TABLESPACE_NAME) C,
       (SELECT TABLESPACE_NAME, SUM(BYTES) BYTES_TOTAL
         FROM   DBA_DATA_FILES
         GROUP  BY TABLESPACE_NAME) D,
       (SELECT A.TABLESPACE_NAME, A.FILE_ID, B.BYTES BYTES_FREE
         FROM   (SELECT TABLESPACE_NAME, FILE_ID,
                         MAX(BLOCK_ID) MAX_DATA_BLOCK_ID
                  FROM   DBA_EXTENTS
                  GROUP  BY TABLESPACE_NAME, FILE_ID) A, DBA_FREE_SPACE B
         WHERE  A.TABLESPACE_NAME = B.TABLESPACE_NAME AND
                A.FILE_ID = B.FILE_ID AND
                B.BLOCK_ID > A.MAX_DATA_BLOCK_ID) E
WHERE  B.TABLESPACE_NAME = C.TABLESPACE_NAME AND
       B.TABLESPACE_NAME = D.TABLESPACE_NAME AND
       BYTES_FULL / BYTES_TOTAL < .7 AND
       B.TABLESPACE_NAME = E.TABLESPACE_NAME AND
       B.FILE_ID = E.FILE_ID;

　　

alter tablespace TABLESPACENAME coalesce

此语句是整合表空间的碎片增加表空间的连续性，但是他不会收缩一个文件的大小的

选择某个表空间中超过N个blocks的segments，通过此语句可以看出那个表占用的空间大　　

SELECT OWNER, SEGMENT_NAME, SEGMENT_TYPE, BLOCKS
FROM   DBA_SEGMENTS
WHERE  TABLESPACE_NAME = 'RISK' AND
       BLOCKS > 1000
ORDER  BY BLOCKS DESC;

　　分析表，得知表的一些信息

analyze table TABLENAME estimate statistics;

SELECT INITIAL_EXTENT, NEXT_EXTENT, MIN_EXTENTS, BLOCKS, EMPTY_BLOCKS
FROM   DBA_TABLES
WHERE  TABLE_NAME = 'xx' AND
       OWNER = 'xx';

　　用alter table ... deallocate unused 命令回收表的空间

alter table user.tablename deallocate unused keep 1k;