OraclePLSQL_性能优化系列17_Oracle Merge Into和Update更新频率

2015-05-21 Created By
BaoXinjian

一、摘要


早先单纯考虑 merge into
只是在特定场合下方便才祭的,今天才发现,merge into 还会比 update
在创新数据时有这么大的改进。

骨子里为,merge
into部分的update和update也未曾啥不同的,不同之地方在用merge
into后实施计划更换了。

merge方法是不过精简,效率最高的道,在雅数据量更新时事先利用这种方法。

  1. 骨干语法

    merge into test1 using test2
    on (test1.id = test2.id)
    when matched then update
    set test1.name = nvl2(test1.name,test2.name,test1.name);

update内联视图方式:使用这种方法必须在test2.id上出主键
(这里十分好掌握,必须保证各一个test1.id针对性诺于test2里只发生雷同漫漫记下,如果test2中生出多条对应之笔录,怎么翻新test1)

还是on (test1.id = test2.id, test1.name =
test2.name ….),通过多栏位对比,确认唯一记录,类似Unique Index

 

  1. 运并行,加快大气数更新:

    merge /+parallel(test1,4)/ into test1 using test2
    on (test1.id = test2.id)
    when matched then update
    set test1.name = nvl2(test1.name,test2.name,test1.name);

 

**亚、测试案例

  • Update / Merge Into**

  1. 创造测试数据

    create table test1 as select * from dba_objects where rownum<=10000;--10000条记录

    create table test2 as select * from dba_objects–73056条记录

 

2.
直Update时间及频率

SQL> alter system flush shared_pool;

System altered.

SQL> alter system flush buffer_cache;

System altered.

SQL> set linesize 400 pagesize 400
SQL> set autot trace
SQL> set timing on
SQL> update test1 t1
  2     set t1.object_name = (select t2.object_name
  3                             from test2 t2
  4                            where t2.object_id = t1.object_id);

10000 rows updated.

Elapsed: 00:06:33.35

Execution Plan
----------------------------------------------------------
   0      UPDATE STATEMENT Optimizer=ALL_ROWS (Cost=2923252 Card=10011 Bytes=790869)
   1    0   UPDATE OF 'TEST1'
   2    1     TABLE ACCESS (FULL) OF 'TEST1' (TABLE) (Cost=40 Card=10011 Bytes=790869)
   3    1     TABLE ACCESS (FULL) OF 'TEST2' (TABLE) (Cost=292 Card=772 Bytes=60988)

Statistics
----------------------------------------------------------
        430  recursive calls
      11122  db block gets
   15275257  consistent gets
       1175  physical reads
    4058752  redo size
        520  bytes sent via SQL*Net to client
        668  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
          7  sorts (memory)
          0  sorts (disk)
      10000  rows processed

 

3.
透过Merge Into时间以及效率 

SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.45
SQL> alter system flush buffer_cache;

System altered.

Elapsed: 00:00:00.71
SQL> merge into test1 t1
  2  using test2 t2
  3  on (t1.object_id = t2.object_id)
  4  when matched then
  5    update set t1.object_name = t2.object_name;

10000 rows merged.

Elapsed: 00:00:00.92

Execution Plan
----------------------------------------------------------
   0      MERGE STATEMENT Optimizer=ALL_ROWS (Cost=1243 Card=10011 Bytes=1321452)
   1    0   MERGE OF 'TEST1'
   2    1     VIEW
   3    2       HASH JOIN (Cost=1243 Card=10011 Bytes=4264686)
   4    3         TABLE ACCESS (FULL) OF 'TEST1' (TABLE) (Cost=40 Card=10011 Bytes=2192409)
   5    3         TABLE ACCESS (FULL) OF 'TEST2' (TABLE) (Cost=292 Card=77163 Bytes=15972741)

Statistics
----------------------------------------------------------
       1224  recursive calls
      10279  db block gets
       1586  consistent gets
       1191  physical reads
    2803872  redo size
        526  bytes sent via SQL*Net to client
        634  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
         12  sorts (memory)
          0  sorts (disk)
      10000  rows processed

 

老三、解析计划


1.
经过Update的辨析计划

SQL> set autot off
SQL> update /*+gather_plan_statistics*/ test1 t1
  2     set t1.object_name = (select t2.object_name
  3                             from test2 t2
  4                            where t2.object_id = t1.object_id);

10000 rows updated.

Elapsed: 00:04:32.81
SQL> select * from table(dbms_xplan.display_cursor(null,null,'iostats'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------
SQL_ID  c8qt9a54qgmqg, child number 0
-------------------------------------
update /*+gather_plan_statistics*/ test1 t1    set t1.object_name =
(select t2.object_name                            from test2 t2
                  where t2.object_id = t1.object_id)

Plan hash value: 3883393169

--------------------------------------------------------------------------------------
| Id  | Operation          | Name  | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------
|   0 | UPDATE STATEMENT   |       |      1 |        |      0 |00:04:32.73 |      10M|
|   1 |  UPDATE            | TEST1 |      1 |        |      0 |00:04:32.73 |      10M|
|   2 |   TABLE ACCESS FULL| TEST1 |      1 |  10011 |  10000 |00:00:00.17 |     133 |
|*  3 |   TABLE ACCESS FULL| TEST2 |  10000 |    772 |  10000 |00:04:31.51 |      10M|
--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - filter("T2"."OBJECT_ID"=:B1)

Note
-----
   - dynamic sampling used for this statement (level=2)


26 rows selected.

Elapsed: 00:00:01.38

 

  1. 经Merge Into的解析计划

    SQL> merge /+gather_plan_statistics/
    2 into test1 t1
    3 using test2 t2
    4 on (t1.object_id = t2.object_id)
    5 when matched then
    6 update set t1.object_name = t2.object_name;

    10000 rows merged.

    Elapsed: 00:00:00.52
    SQL> select * from table(dbms_xplan.display_cursor(null,null,’iostats’));

    PLAN_TABLE_OUTPUT

    SQL_ID 9n4tc6tvwaj9c, child number 0

    merge /+gather_plan_statistics/ into test1 t1 using test2 t2 on
    (t1.object_id = t2.object_id) when matched then update set
    t1.object_name = t2.object_name

    Plan hash value: 818823782


    | Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |

    | 0 | MERGE STATEMENT | | 1 | | 0 |00:00:00.47 | 11458 |
    | 1 | MERGE | TEST1 | 1 | | 0 |00:00:00.47 | 11458 |
    | 2 | VIEW | | 1 | | 10000 |00:00:00.33 | 1179 |
    |* 3 | HASH JOIN | | 1 | 10011 | 10000 |00:00:00.25 | 1179 |
    | 4 | TABLE ACCESS FULL| TEST1 | 1 | 10011 | 10000 |00:00:00.08 | 133 |

    | 5 | TABLE ACCESS FULL| TEST2 | 1 | 77163 | 73056 |00:00:00.26 | 1046 |

    Predicate Information (identified by operation id):

    3 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")
    

    Note

    - dynamic sampling used for this statement (level=2)
    
28 rows selected.

Elapsed: 00:00:00.15

 

季、结果分析


  1. 测试结果相比:update和merge into
    都更新1w长达记下,

update耗时6分钟,逻辑读消耗15275257;

merge into
耗时6秒钟,消耗逻辑读1586,相差太大了。

 

2.
实际上看在执行计划,这个结果也杀轻掌握:

update采用的近乎nested
loop的法,对创新的每一样行,都见面对查询的阐明扫描一次;

merge into这里选择的凡hash
join,则针对各个张表都是开了扳平赖 full table
scan,对各国张表都只是扫描一不好。

 

3.
Oracle官方建议,在十分数据更新过程中,也是经采用Merge
Into代替Update

 

Thanks and
Regards

参考: http://blog.csdn.net/xiexbb/article/details/4242063

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