由於遇到某個系統需要新新增LOB欄位，並且會有大量的插入刪除操作，所以需要確認下lob欄位在

大量資料操作之後總的體積大小變化是怎樣的。猜想lob欄位的大小並不會自動收縮，是持續增長的，需要手動干預收縮空間

--測試1 測試disable storage in row下的lob欄位
--create table建立測試表
create table T_LOB_TEST
(
  id         number(10) not null,
  xml_content BLOB,
  comm       VARCHAR2(5)
)
lob(xml_content) store as
(disable storage in row
nocache logging)
;

--插入資料
declare 
i number(10);
begin
 for i in 1..1000
 loop
  insert into T_LOB_TEST values(i,to_blob('11111000011111000100001110000101010101000001000000011111100000000000000000111111111111100000000111111'),'comm');
 end loop;
 commit;
end;
/

--查詢佔用空間
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');


SEGMENT_NAME             BYTES/1024
T_LOB_TEST               64
SYS_IL0000346640C00002$$ 128
SYS_LOB0000346640C00002$$ 9216



--刪除部分資料
SQL> delete from T_LOB_TEST where id>200;
 
800 rows deleted
 
SQL> commit;
 
Commit complete
 
SQL> 


--再次查詢佔用空間，並未變化
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');

SEGMENT_NAME             BYTES/1024
T_LOB_TEST               64
SYS_IL0000346640C00002$$ 128
SYS_LOB0000346640C00002$$ 9216



--再次插入資料
declare 
i number(10);
begin
 for i in 201..1000
 loop
  insert into T_LOB_TEST values(i,to_blob('11111000011111000100001110000101010101000001000000011111100000000000000000111111111111100000000111111'),'comm');
 end loop;
 commit;
end;
/

--再查詢佔用空間，發現佔用空間變大了
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');


SEGMENT_NAMEBYTES/1024
T_LOB_TEST64
SYS_IL0000346640C00002$$192
SYS_LOB0000346640C00002$$15360


--結論1：
--lob欄位空間不會重複使用。重複刪除插入，lob欄位持續增長


--處理方法：需要壓縮空間
ALTER TABLE r_zhangry.T_LOB_TEST  MODIFY LOB (xml_content) (SHRINK SPACE);

--查詢佔用空間，變成初始狀態了
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');

SEGMENT_NAMEBYTES/1024
T_LOB_TEST64
SYS_IL0000346640C00002$$320
SYS_LOB0000346640C00002$$960





--測試2 測試非disable storage in row模式下
--該模式為預設模式，既小於4k的資料不會存在lob中，只有大於4k的資料才會存在lob欄位中

--建立測試表
create table T_LOB_TEST
(
  id         number(10) not null,
  xml_content BLOB,
  comm       VARCHAR2(5)
)
;


--插入資料
declare 
i number(10);
begin
 for i in 1..1000
 loop
  if  mod(i,3) != 0 then
  insert into T_LOB_TEST values(i,to_blob('11111000011111000100001110000'),'comm');
  else
  insert into T_LOB_TEST (select i,b.payload,'comm' from mid_opr.JBM_MSG b where rownum<2);
  end if;
  commit;
 end loop;
 commit;
end;
/


--查詢佔用空間
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');


SEGMENT_NAMEBYTES/1024
T_LOB_TEST128
SYS_IL0000346643C00002$$64
SYS_LOB0000346643C00002$$16384



--刪除部分資料
SQL> delete from T_LOB_TEST where id>200;
 
800 rows deleted
 
SQL> commit;
 
Commit complete
 
SQL> 



--再次查詢佔用空間，並無變化
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');


SEGMENT_NAMEBYTES/1024
T_LOB_TEST128
SYS_IL0000346643C00002$$64
SYS_LOB0000346643C00002$$16384



--再次插入資料
declare 
i number(10);
begin
 for i in 201..1000
 loop
  if  mod(i,3) != 0 then
  insert into T_LOB_TEST values(i,to_blob('11111000011111000100001110000'),'comm');
  else
  insert into T_LOB_TEST (select i,b.payload,'comm' from mid_opr.JBM_MSG b where rownum<2);
  end if;
  commit;
 end loop;
 commit;
end;
/

--再查詢佔用空間，佔用空間變大了
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');


SEGMENT_NAMEBYTES/1024
T_LOB_TEST128
SYS_IL0000346643C00002$$64
SYS_LOB0000346643C00002$$29696



結論2：
--lob欄位空間不會重複使用。重複刪除插入，lob欄位持續增長



處理方法：
--需要壓縮空間
ALTER TABLE r_zhangry.T_LOB_TEST  MODIFY LOB (xml_content) (SHRINK SPACE);

--再次查詢空間，結果變為初始狀態
select segment_name,bytes/1024 from user_segments where segment_name='T_LOB_TEST'
or segment_name in (select segment_name from user_lobs where table_name='T_LOB_TEST')
or segment_name in (select index_name from user_lobs where table_name='T_LOB_TEST');


SEGMENT_NAMEBYTES/1024
T_LOB_TEST128
SYS_IL0000346643C00002$$64
SYS_LOB0000346643C00002$$16384