Oracle dba_data_files dba_segments dba_free_space

1, dba_data_files,dba_segments,dba_free_space

得出结论:一般情况下(没有drop表的时候):dba_data_files bytes = (dba_segments bytes + dba_free_space bytes)

SQL>

select TABLESPACE_NAME,
BYTES/1024/1024,BLOCKS,
AUTOEXTENSIBLE,
MAXBYTES,
MAXBLOCKS,
INCREMENT_BY,
USER_BYTES,
USER_BLOCKS
from   dba_data_files
where  tablespace_name='TS_20120626';

TABLESPACE_NAME BYTES/1024/1024 BLOCKS AUT MAXBYTES MAXBLOCKS INCREMENT_BY USER_BYTES USER_BLOCKS

-------------------- --------------- ---------- --- ---------- ---------- ------------ ---------- -----------

TS_20120626 120 15360 YES 3.4360E+10 4194302 12800 125763584 15352

SQL>select OWNER,SEGMENT_NAME,TABLESPACE_NAME,BYTES/1024/1024,BLOCKS fromdba_segmentswhere
TABLESPACE_NAME='TS_20120626';

OWNER SEGMENT_NAME TABLESPACE_NAME BYTES/1024/1024 BLOCKS

----------------------- ------------------------------ ------------------------------ --------------- ----------

USER_20120626 TB_20120626_001 TS_20120626 61 7808

SQL>select
tablespace_name,bytes/1024/1024||' MB' Total_Free fromdba_free_spacewhere tablespace_name='TS_20120626';

TABLESPACE_NAME TOTAL_Free

------------------------------ -------------------------------------------

TS_20120626 58.9375 MB

2, delete,truncate,drop对空间的变化影响

delete表数据,对上述3个视图查询没有任何变化,满足上述相等原则.

truncate表数据,表空间一次性回收,dba_free_space增加,dba_segments减少,让满足上述相等原则.

drop表,表空间一次性回收,但dba_segment会多出个回收站,但实际上dba_free_segment也把回收站的那部分空间计算在内了,所以回收站的内容实际也是可以使用的部分,表面上看这个等式不成立了,但实质上做了些改变,看下面的例子.

SQL>select TABLESPACE_NAME,BYTES/1024/1024,BLOCKS, AUTOEXTENSIBLE,MAXBYTES,MAXBLOCKS,INCREMENT_BY,USER_BYTES,USER_BLOCKS
from dba_data_files where tablespace_name='TS_20120626';

TABLESPACE_NAME BYTES/1024/1024 BLOCKS AUT MAXBYTES MAXBLOCKS INCREMENT_BY USER_BYTES USER_BLOCKS

------------------------- --------------- ---------- --- ---------- ---------- ------------ ---------- -----------

TS_20120626 320
40960 YES 3.4360E+10 4194302 12800 335478784 40952

SQL>select OWNER,SEGMENT_NAME,TABLESPACE_NAME,BYTES/1024/1024,BLOCKS from dba_segments where TABLESPACE_NAME='TS_20120626';

OWNER SEGMENT_NAME TABLESPACE_NAME BYTES/1024/1024 BLOCKS

----------------------- ----------------------------- ------------------- --------------- ----------

USER_20120626 TB_20120626_002 TS_20120626 168 21504

USER_20120626 TB_20120626_001 TS_20120626 .0625
8 //truncate的表数据

USER_20120626 BIN$w1rH4uiTmbbgQKjANgEvlg==$0 TS_20120626 28
3584//drop后的回收站部分

SQL>select tablespace_name,bytes/1024/1024||' MB' Total_Free from dba_free_space where tablespace_name='TS_20120626';

TABLESPACE_NAME TOTAL_FREE

------------------------------ -------------------------------------------

TS_20120626 27.9375 MB//truncate后,一次性回收的部分.

TS_20120626 95.9375 MB

TS_20120626 .0625 MB //drop后,从这里开始都是回收站的部分.这里和上面的BIN$w1rH4uiTmbbgQKjANgEvlg==$0是同一空间

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 .0625 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

TS_20120626 1 MB

45 rows selected.

将上述查询结果用tablespace_name分组加起来

SQL>select tablespace_name,count(tablespace_name) ,sum(bytes/1024/1024)||' MB' Total_Free from dba_free_space where tablespace_name='TS_20120626'
group by tablespace_name;

TABLESPACE_NAME COUNT(TABLESPACE_NAME) TOTAL_FREE

------------------------------ ---------------------- -------------------------------------------

TS_20120626 45151.875MB

所以上述等式需要改为(有drop时):dba_data_files bytes = (dba_segments bytes + dba_free_space bytes- dba_segment回收站部分)