Oracle使用hash分區優化分析函數查詢

2009-05-19 14:34:52

本文將介紹Oracle使用hash分區優化分析函數查詢，一般需要通過創建一個分區表和普通表，插入數據等步驟來進行優化。

在ORACLE中的分析函數都是基于某幾個字段劃分計算窗口，然后在窗口內進行聚合，排名，等等計算。我想如果我們數據表的hash分區字段與分析函數中的partition by 字段一致的時候，應該可以大大加快分析函數的運行效率。因為每個分區上的數據可以單獨進行運算。互不干涉，下面試驗來驗證我的想法.

***步：創建一個分區表和普通表，表結構與DBA_OBJECTS一致：

create table t_partition_hash(
object_name varchar2(128),
subobject_name varchar2(30),
object_id number,
data_object_id number,
object_type varchar2(19),
created date,
last_ddl_time date,
timestamp varchar2(19),
status varchar2(7),
temporary varchar2(1),
generated varchar2(1),
secondary varchar2(1)
)
 partition by hash(object_type)(
 partition t_hash_p1 tablespace USERS,
 partition t_hash_p2 tablespace USERS,
 partition t_hash_p3 tablespace USERS,
 partition t_hash_p4 tablespace USERS,
 partition t_hash_p5 tablespace USERS,
 partition t_hash_p6 tablespace USERS,
 partition t_hash_p7 tablespace USERS,
 partition t_hash_p8 tablespace USERS
 );
create table t_big_hash(
object_name varchar2(128),
subobject_name varchar2(30),
object_id number,
data_object_id number,
object_type varchar2(19),
created date,
last_ddl_time date,
timestamp varchar2(19),
status varchar2(7),
temporary varchar2(1),
generated varchar2(1),
secondary varchar2(1)
);

第二步：準備數據，從dba_object中把數據插入到兩個表。總共插入數據1610880。

insert into t_partition_hash select * from dba_objects;

第三步：本采用RANK函數對兩個表進行查詢。

begin
insert into  t_rank
select object_id, 
rank() over (partition by object_type order by object_id)  r_object_id,
rank() over (partition by object_type order by subobject_name) r_subobject_name ,
rank() over (partition by object_type order by created) r_created,
rank() over (partition by object_type order by last_ddl_time) r_last_ddl_time ,
rank() over (partition by object_type order by status) r_object_type
 from t_partition_hash;
end;

使用hash分區表總共執行5次的運行時間分別為：46.156s,33.39s,40.516s 34.875s 38.938s.

begin
insert into  t_rank
select object_id, 
rank() over (partition by object_type order by object_id)  r_object_id,
rank() over (partition by object_type order by subobject_name) r_subobject_name ,
rank() over (partition by object_type order by created) r_created,
rank() over (partition by object_type order by last_ddl_time) r_last_ddl_time ,
rank() over (partition by object_type order by status) r_object_type
 from t_big_table;
end; 
使用非分區表執行5次的執行時間分別為：141.954s，89.656s，77.906s，98.5s，75.906s.

由此可見采用有效的HASH分區表可以有效提升分析函數在oracle中的執行效率。我相信隨著數據量的增加，將會有更明顯的效果，回頭再測試一個項目中遇到的類似問題。

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責任編輯：彭凡來源： ITPUB