dba_extents和dba_segments不一致问题及原因

今天发现这两个视图查询出来的空间有差异，通过网上查找，看到eygle大师的博客以及其他网友的资料，简单总结一下：

以下是转载网站：

http://www.eygle.com/archives/2009/08/dba_extents_dba_segments.html

http://www.dbafan.com/blog/?p=146

看到都是从Metalink上得到答案，一句话，对于我们使用dba_extents时绝对正确的，

至于两者差距主要是由于个并行索引创建、频繁的DELETE/INSERT等操作中，Segemnt Header信息未能及时更新，导致段头记录的空间值和Extent Map不一致。

下列语句可以查出不一致的段:

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 
and s.owner not like 'SYS%' 
and ((s.blocks <> e.blocks) or (s.extents <> e.extents) or (s.bytes <> e.bytes));

解决方法是运行procedure: TABLESPACE_FIX_SEGMENT_EXTBLKS

DBMS_SPACE_ADMIN.TABLESPACE_FIX_SEGMENT_EXTBLKS(‘tablespace_name’);

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.

对于application并没有什么影响，只是会影响一些依赖于dba_segments做监控的monitoring