dba_segments和dba_tables的不同

create table tset as select * from dba_objects;

select count(*) from tset;

select table_name,blocks,empty_blocks from dba_tables

where table_name=’TSET’;

select segment_name,bytes,blocks,extents from dba_segments

where segment_name=’TSET’;

问题来了，从dba_tables查询的blocks是空的，不按常理出牌啊~~什么鬼，什么鬼

select table_name,blocks,empty_blocks,last_analyzed from dba_tables

where table_name=’TSET’;

last_analyzed是分析的时间，为空值表示没有分析，所以执行语句分析下看看

analyze table tset compute statistics;

1071+80=1151

好像还少一个blocks，不是好像，就是少一个block。（先放这吧，不确定能找到为什么）。

以上是我发现dba_tables和dba_segments的blocks数量不一致后查询网络得出的；

大概个人总结以下：

1.dba_segments中的blocks对应的是dba_tables中的blocks+empty_blocks

2.

The dba_tables view describes a "logical" structure whiledba_segments describes the "physical" data segment, like a data file.

Also, columns like "blocks" are different between dba_tables and dba_segments.  In dba_tables, the "blocks" are calculated when you run dbms_stats, while indba_segments, "blocks" is the actual number of blocks used by the object on disk.

(不解释，解释不了，我感觉只是感觉理解了)，附上链接：http://www.dba-oracle.com/t_difference_dba_tables_dba_segments.htm

 

oracle社区里有个不是使用CTAS创建表来说明dba_segments和dba_tables不一致的问题，我重复一遍吧：

1. create table tset1 as select * from dba_objects where 1=0;

select segment_name,bytes,blocks,extents from dba_segments

where segment_name=’TSET1’；

插播：

TSET1表的行数为0；默认分配一个extent，一个extent=8 blocks,一个block=8k（65536/1024/8）

oracle 11g不是延迟段分配的吗（默认）？

好吧，先不管了，下次再说吧，插播到此结束。

2.select table_name,blocks,empty_blocks from dba_tables where table_name=’TSET1’;

   analyze table tset1 compute statistics;

   select table_name,blocks,empty_blocks from dba_tables where table_name=’TSET1’;

3.insert into tset1 select * from dba_objects;

   commit;

4. select segment_name,bytes,blocks,extents from dba_segments

    where segment_name=’TSET1’;

    select table_name,blocks,empty_blocks from dba_tables

    where table_name=’TSET1’;

    analyze table tset1 comput statistics;

    select table_name,blocks,empty_blocks from dba_tables

    where table_name=’TSET1’;

1068+83=1151,还是不等于1152

附上oracle社区的链接，上面的测试结果是相等的哦！

https://community.oracle.com/thread/582356?start=0&tstart=0