检测表是否需要shrink,Segment advisor
exec DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO;
select a.owner || '.' || a.table_name "Table",a.num_rows,a.avg_row_len,b.inserts,b.deletes,a.num_rows+nvl(b.inserts,0)-nvl(b.deletes,0) total_rows,
round(a.avg_row_len*(a.num_rows+nvl(b.inserts,0)-nvl(b.deletes,0))/1024/1024,4) "Calculate_Sizle(Mb)",c.bytes/1024/1024 "Segment_Size(Mb)"
from dba_tables a left join dba_tab_modifications b
on a.owner=b.table_owner and a.table_name=b.table_name inner join dba_segments c on a.owner=c.owner and a.table_name=c.segment_name
where a.last_analyzed is not null and a.partitioned='NO' and a.owner not in
('SYS', 'SYSTEM', 'SYSMAN', 'DMSYS', 'OLAPSYS','XDB', 'EXFSYS', 'CTXSYS', 'WMSYS', 'DBSNMP', 'ORDSYS', 'OUTLN', 'TSMSYS', 'MDSYS')
and (a.avg_row_len*(a.num_rows+nvl(b.inserts,0)-nvl(b.deletes,0)))/c.bytes<0.5;
上面的脚本(注意，该脚本只能检测被分析过的表，另外我也没有考虑分区表)可以初步判断数据库中所有表是否需要shrink，得到关于表的概要信息之后，我们可以利用10g中的Segment advisor来判断该表是否需要shrink，可以用oem来调用segment advisor，不过很多情况下oem并没有打开，所以这里介绍如何手动执行Segment advisor。
Segment advisor 例子:
SQL> show user
User is "robinson"
SQL> create table test as select * from dba_objects;
Table created
SQL> insert into test select * from dba_objects;
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> /
49792 rows inserted
SQL> select owner,segment_name,segment_type,bytes/1024/1024 "Size(Mb)" from dba_segments where segment_name='TEST';
OWNER SEGMENT_NA SEGMENT_TYPE Size(Mb)
---------- ---------- ------------------ ----------
ROBINSON TEST TABLE 60
SQL> commit;
Commit complete
SQL> select count(*) from test;
COUNT(*)
----------
547712
SQL> delete from test where rownum<547712/2;
273855 rows deleted
SQL> commit;
Commit complete
SQL> variable task_id number;
SQL> begin
2 declare
3 object_id number;
4 name varchar2(100);
5 task_desc varchar2(100);
6 begin
7 name := 'test';
8 task_desc := 'Segment Advisor TEST';
9 dbms_advisor.create_task(advisor_name => 'Segment Advisor',
10 task_id => :task_id,
11 task_name => name,
12 task_desc => task_desc
13 );
14 dbms_advisor.create_object(task_name => name,
15 object_type => 'TABLE',
16 attr1 => 'ROBINSON',
17 attr2 => 'TEST',
18 attr3 => NULL,
19 attr4 => NULL,
20 attr5 => NULL,
21 object_id =>object_id
22 );
23 dbms_advisor.set_task_parameter(task_name => name,
24 parameter => 'recommend_all',
25 value => 'TRUE'
26 );
27 dbms_advisor.execute_task(task_name => name);
28 end;
29 end;
30 /
PL/SQL procedure successfully completed
task_id
---------
560
SQL> col task_name format a8
SQL> col segname format a8
SQL> col partition format a8
SQL> col type format a8
SQL> col message format a100
SQL> select af.task_name, ao.attr2 segname, ao.attr3 partition, ao.type, af.message
2 from dba_advisor_findings af, dba_advisor_objects ao
3 where ao.task_id = af.task_id
4 and ao.object_id = af.object_id
5 and ao.owner = 'ROBINSON';
TASK_NAM SEGNAME PARTITIO TYPE MESSAGE
-------- -------- -------- -------- ----------------------------------------------------------------------------------------------------
test TEST TABLE Enable row movement of the table ROBINSON.TEST and perform shrink, estimated savings is 28451785 byt
es.
SQL> select 28451785/1024/1024 from dual;
28451785/1024/1024
------------------
27.1337366104126
从Segment advisor里面得到如果对表进行shrink 可以节约27M的空间，根据例子的操作步骤也可以得出这个结论，因为我删除了一般的数据
，在未删除之前表test占用了60M。由此可见Segment advisor的结果还是比较准确的。
查看task信息:
select * from dba_advisor_tasks where advisor_name!='ADDM';
删除task:
SQL> exec dbms_advisor.delete_task(task_name => 'test');
PL/SQL procedure successfully completed