dba_segments和dba_tables的不同

create table tset as select * from dba_objects;

select count(*) from tset;

dba_segments和dba_tables的不同_第1张图片

select table_name,blocks,empty_blocks from dba_tables

where table_name=’TSET’;

image

select segment_name,bytes,blocks,extents from dba_segments

where segment_name=’TSET’;

image

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’;

image

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;

dba_segments和dba_tables的不同_第2张图片

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’;

dba_segments和dba_tables的不同_第3张图片

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)

dba_segments和dba_tables的不同_第4张图片

oracle 11g不是延迟段分配的吗(默认)?

dba_segments和dba_tables的不同_第5张图片

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’;

dba_segments和dba_tables的不同_第6张图片

3.insert into tset1 select * from dba_objects;

   commit;

dba_segments和dba_tables的不同_第7张图片

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’;

dba_segments和dba_tables的不同_第8张图片

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

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