發現dba_segments和dba_extents中統計段空間大小居然不一樣

最近在測試系統上發現dba_segments和dba_extents中統計段空間大小居然不一樣

SQL> select bytes,blocks,extents from dba_segments where segment_name='PROFILE' and owner='NAP3';

BYTES BLOCKS EXTENTS
---------- ---------- ----------
0 0 0

SQL> select bytes,blocks,extent_id from dba_extents where segment_name='PROFILE' and owner='NAP3';

BYTES BLOCKS EXTENT_ID
---------- ---------- ----------
167772160 20480 0


在metalink上搜尋到如下資料： Doc ID: Note:463101.1
HOW TO DISCOVER AND FIX THE MISTMATCH BETWEEN DBA_SEGMENTS AND DBA_EXTENTS DICTIONARY VIEWS

裡面講到當DML/DDL操作(parallel index creation, frequent deletes/inserts)會導致這種不一致，
導致dba_segments中的不正確, 所以dba_extents中記錄的分配給段的空間值才是可信的值。。

解決方法是執行一個Oracle internal的未寫入文件的procedure:

[@more@]

DBMS_SPACE_ADMIN.TABLESPACE_FIX_SEGMENT_EXTBLKS('<tablespace_name>');

（注意要把COMPATIBLE設定到10.0.0以上）

Issuing DBMS_SPACE_ADMIN.TABLESPACE_FIX_SEGMENT_EXTBLKS fixes the DBA_SEGMENTS values. The tablespace
must be kept
online and read/write when this procedure is called. Runing this procedure requires
COMPATIBLE parameter to be set to 10.0.0.0 or greater.
The procedure fixes extents, blocks and bytes in the segment headers to synchronize seg$ and
segment header entries.
It holds the allocation enqueue for the tablespace till the command
is completed and this may delay some sort of operations in this tablespace (new extent allocation,
deallocate extent, etc.). So it needs to be run during an idle period.


可以透過如下語句來檢查系統中所有不一致的segment：

select
/*+ RULE */ s.tablespace_name, s.segment_name segment, s.partition_name,
s.owner owner, s.segment_type,
s.blocks sblocks, e.blocks eblocks,
s.extents sextents, e.extents eextents, s.bytes sbytes, e.bytes ebytes
from
dba_segments s,
(select count(*) extents, sum(blocks) blocks, sum(bytes) bytes, segment_name,
partition_name, segment_type, owner
from dba_extents
group
by segment_name,partition_name,segment_type,owner) e
where s.segment_name=e.segment_name
and s.owner = e.owner
and (s.partition_name = e.partition_name or s.partition_name is
null)
and s.segment_type = e.segment_type