shrink 实例

create table t nologging
as
select o.* from
(select * from dba_objects where rownum <10001) o,
(select * from dba_objects where rownum <101) o2
order by o.object_id;

 

select bytes/1024/1024 from user_segments where segment_name='T';
T大小为104M

 

select count(*) from t;

 

delete from t where mod(object_id,2)=0;

 

commit;

 

select count(*) from t;

 

alter table t enable row movement;

 

select a.name,b.value
from v$statname a,v$mystat b
where a.statistic#=b.statistic# and a.name='redo size';

shrink之前redo size 173M

 

alter table t shrink space;

 

select a.name,b.value
from v$statname a,v$mystat b
where a.statistic#=b.statistic# and a.name='redo size';

shrink之后 redo size 356M

 

select bytes/1024/1024 from user_segments where segment_name='T';
46M

 

分析table

 analyze table TBLMINNO compute statistics;

 

select table_name,num_rows,AVG_ROW_LEN,BLOCKS,EMPTY_BLOCKS from dba_tables
where table_name='TBLMINNO';