【读书笔记】【收获，不止Oracle】不同连接类型表下，驱动顺序对查询性能的影响
2014-08-27 22:31
573 查看
本次试验用于探究 嵌套循环，哈希连接，排序合并这三种类型下，驱动表顺序的研究。
一、嵌套循环(Nested Loops Join)
1.t1为主表，t2为从表(t1表先访问)
2.t1为从表，t2为主表时(t2表先访问)
3.结论：
3.1 根据驱动表的访问顺序不同，Buffers产生的差异是巨大的。
3.2 T1为驱动表时，T2被访问1次。而T2为驱动表时，T1被访问10000次。
3.3 循环嵌套表应注意驱动表的顺序。小的结果集先访问，大的结果集后访问。才能使得被驱动表的访问次数降到最低，从而提升性能。
二、哈希连接(Hash Join)
1.t1为主表，t2为从表(t1表先访问)
2.t1为从表，t2为主表时(t2表先访问)
3.结论
3.1 根据驱动表的访问顺序不同，Buffers相同，但Used-Mem的差别很大。
三、排序合并(Merge Sort Join)
1.t1为主表，t2为从表(t1表先访问)
3.1 无论t1先访问还是后访问Buffer,Status,Used-Mem都是一样的。所以排序合并下，驱动表的访问顺序无关。排序合并连接无驱动顺序。
一、嵌套循环(Nested Loops Join)
1.t1为主表，t2为从表(t1表先访问)
select /*+leading(t1) use_nl(t2)*/* from t1,t2 where t1.id = t2.t1_id and t1.n = 19;
SCOTT@ orclselect * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID 4j97842y306uk, child number 0
-------------------------------------
select /*+leading(t1) use_nl(t2)*/* from t1,t2 where t1.id = t2.t1_id and
t1.n = 19
Plan hash value: 1967407726
-------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 1014 |
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|* 2 | TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 8 |
|* 3 | TABLE ACCESS FULL| T2 | 1 | 1 | 1 |00:00:00.01 | 1006 |
-------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("T1"."N"=19)
3 - filter("T1"."ID"="T2"."T1_ID")
Note
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-----
- dynamic sampling used for this statement
25 rows selected.2.t1为从表，t2为主表时(t2表先访问)
select /*+leading(t2) use_nl(t1)*/*
from t1,t2
where t1.id = t2.t1_id
and t1.n = 19;
SCOTT@ orcl>select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID 6uqqzgzs7y35f, child number 0
-------------------------------------
select /*+leading(t2) use_nl(t1)*/* from t1,t2 where t1.id = t2.t1_id and
t1.n = 19
Plan hash value: 4016936828
-------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:02.75 | 701K|
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 2 | TABLE ACCESS FULL| T2 | 1 | 102K| 100K|00:00:00.30 | 1006 |
|* 3 | TABLE ACCESS FULL| T1 | 100K| 1 | 1 |00:00:01.98 | 700K|
-------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter(("T1"."N"=19 AND "T1"."ID"="T2"."T1_ID"))
Note
-----
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
- dynamic sampling used for this statement
24 rows selected.3.结论：
| Starts | Buffers | ||||
| 第一次 | 主 | T1 | 1 | 8 | 1014 |
| 从 | T2 | 1 | 1006 | ||
| 第二次 | 主 | T2 | 1 | 1006 | 701K |
| 从 | T1 | 100K | 700k |
3.2 T1为驱动表时，T2被访问1次。而T2为驱动表时，T1被访问10000次。
3.3 循环嵌套表应注意驱动表的顺序。小的结果集先访问，大的结果集后访问。才能使得被驱动表的访问次数降到最低，从而提升性能。
二、哈希连接(Hash Join)
1.t1为主表，t2为从表(t1表先访问)
select /*+leading(t1) use_hash(t2)*/*
from t1,t2
where t1.id = t2.t1_id
and t1.n = 19;
SCOTT@ orcl>select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID c7tdkmk355c8n, child number 0
-------------------------------------
select /*+leading(t1) use_hash(t2)*/* from t1,t2 where t1.id = t2.t1_id and t1.n = 19
Plan hash value: 1838229974
----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------
|* 1 | HASH JOIN | | 1 | 1 | 1 |00:00:00.74 | 1013 | 741K| 741K| 328K (0)|
|* 2 | TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 7 | | | |
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 3 | TABLE ACCESS FULL| T2 | 1 | 102K| 100K|00:00:00.20 | 1006 | | | |
----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("T1"."ID"="T2"."T1_ID")
2 - filter("T1"."N"=19)
Note
-----
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
- dynamic sampling used for this statement
24 rows selected.2.t1为从表，t2为主表时(t2表先访问)
select /*+leading(t2) use_hash(t1)*/*
from t1,t2
where t1.id = t2.t1_id
and t1.n = 19;
SCOTT@ orcl>select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID 5mszurvg6jrxx, child number 0
-------------------------------------
select /*+leading(t2) use_hash(t1)*/* from t1,t2 where t1.id = t2.t1_id and t1.n = 19
Plan hash value: 2959412835
----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------
|* 1 | HASH JOIN | | 1 | 1 | 1 |00:00:00.89 | 1013 | 9471K| 1956K| 10M (0)|
| 2 | TABLE ACCESS FULL| T2 | 1 | 102K| 100K|00:00:00.20 | 1005 | | | |
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|* 3 | TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 8 | | | |
----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("T1"."ID"="T2"."T1_ID")
3 - filter("T1"."N"=19)
Note
-----
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
- dynamic sampling used for this statement
24 rows selected.3.结论
| Starts | Buffers | Used-Mem | ||||
| 第一次 | 主 | T1 | 1 | 7 | 1013 | 328K |
| 从 | T2 | 1 | 1006 | |||
| 第二次 | 主 | T2 | 102K | 1005 | 1013 | 10M |
| 从 | T1 | 1 | 8 |
三、排序合并(Merge Sort Join)
1.t1为主表，t2为从表(t1表先访问)
select /*+leading(t1) use_merge(t2)*/*
from t1,t2
where t1.id = t2.t1_id
and t1.n = 19;
SCOTT@ orcl>select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID aw04dp4k1q1x7, child number 0
-------------------------------------
select /*+leading(t1) use_merge(t2)*/* from t1,t2 where t1.id = t2.t1_id and t1.n = 19
Plan hash value: 412793182
-----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------
| 1 | MERGE JOIN | | 1 | 1 | 1 |00:00:00.43 | 1012 | | | |
| 2 | SORT JOIN | | 1 | 1 | 1 |00:00:00.01 | 7 | 2048 | 2048 | 2048 (0)|
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|* 3 | TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 7 | | | |
|* 4 | SORT JOIN | | 1 | 102K| 1 |00:00:00.43 | 1005 | 9124K| 1177K| 8110K (0)|
| 5 | TABLE ACCESS FULL| T2 | 1 | 102K| 100K|00:00:00.20 | 1005 | | | |
-----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("T1"."N"=19)
4 - access("T1"."ID"="T2"."T1_ID")
filter("T1"."ID"="T2"."T1_ID")
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Note
-----
- dynamic sampling used for this statement
27 rows selected.2.t1为从表，t2为主表时(t2表先访问)select /*+leading(t2) use_merge(t1)*/*
from t1,t2
where t1.id = t2.t1_id
and t1.n = 19;
SCOTT@ orcl>select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID 79yag6bg8z2zr, child number 0
-------------------------------------
select /*+leading(t2) use_merge(t1)*/* from t1,t2 where t1.id = t2.t1_id and t1.n = 19
Plan hash value: 1792967693
-----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------
| 1 | MERGE JOIN | | 1 | 1 | 1 |00:00:00.86 | 1012 | | | |
| 2 | SORT JOIN | | 1 | 102K| 20 |00:00:00.86 | 1005 | 9124K| 1177K| 8110K (0)|
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 3 | TABLE ACCESS FULL| T2 | 1 | 102K| 100K|00:00:00.20 | 1005 | | | |
|* 4 | SORT JOIN | | 20 | 1 | 1 |00:00:00.01 | 7 | 2048 | 2048 | 2048 (0)|
|* 5 | TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 7 | | | |
-----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("T1"."ID"="T2"."T1_ID")
filter("T1"."ID"="T2"."T1_ID")
5 - filter("T1"."N"=19)
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Note
-----
- dynamic sampling used for this statement
27 rows selected.3.结论| Starts | Buffers | Used-Mem | |||
| 第一次 | 主 | SORT1 | 1 | 1 | 2048 |
| 从 | SORT2 | 1 | 102K | 8110 | |
| 第二次 | 主 | SORT2 | 1 | 102K | 8110 |
| 从 | SORT1 | 1 | 1 | 2048 |
内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理 
相关文章推荐
- 【读书笔记】【收获，不止Oracle】不同类型下表连接限制的对比
- 32.读书笔记收获不止Oracle之表链接的驱动顺序
- 30.读书笔记收获不止Oracle之表的哈希连接
- SQL Server中多表连接时驱动顺序对性能的影响
- 36.读书笔记收获不止Oracle之表哈希、合并排序连接与索引
- SQL Server中多表连接时驱动顺序对性能的影响
- 33.读书笔记收获不止Oracle之表连接的排序分析
- 5.读书笔记收获不止Oracle之 插入表性能示例
- 31.读书笔记收获不止Oracle之表的合并排序连接
- 34.读书笔记收获不止Oracle之表连接场景对比
- SQL Server中多表连接时驱动顺序对性能的影响
- 29.读书笔记收获不止Oracle之表的循环嵌套连接
- 35.读书笔记收获不止Oracle之嵌套循环表连接与索引
- oracle中Where子句的条件顺序对性能的影响
- 【读书笔记】【收获，不止Oracle】索引组织表
- Oracle 多表查询连接的三种类型
- Oracle使用子查询，和左连接查询同样结果性能差距。
- oracle 聚簇因子对查询性能的影响
- oracle 聚簇因子对查询性能的影响
- Oracle 多表 连接 顺序 与 性能关系 测试