最近在测试系统上发现dba_segments和dba_extents中统计段空间大小居然不一样

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上搜索到如下资料： Doc ID: Note:463101.1
HOW TO DISCOVER AND FIX THE MISTMATCH BETWEEN DBA_SEGMENTS AND DBA_EXTENTS DICTIONARY VIEWS

里面讲到当DML/DDL操作(parallel index creation, frequent deletes/inserts)会导致这种不一致，
导致dba_segments中的不正确, 所以dba_extents中记录的分配给段的空间值才是可信的值。。

解决方法是执行一个Oracle internal的未写入文档的procedure:

DBMS_SPACE_ADMIN.TABLESPACE_FIX_SEGMENT_EXTBLKS('<tablespace_name>');

（注意要把COMPATIBLE设置到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.

可以通过如下语句来检查系统中所有不一致的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

本文转自 vfast_chenxy 51CTO博客，原文链接：http://blog.51cto.com/chenxy/744490，如需转载请自行联系原作者