[20160125]闭包传递问题.txt
--所谓闭包传递是指sql语句的谓词条件A=B and B=C 可以推出 A=C. oracle 的 优化器能够利用这个特性优化sql语句。
--但是这些依旧存在一些问题，在电子书<Apress.Expert.Oracle.SQL.Optimization.Deployment.and.Statistics.1430259779.pdf>
--提到一个例子，无法实现闭包传递。自己重复测试看看：
1.环境：
SCOTT@book> @ &r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
CREATE TABLE t3 AS SELECT ROWNUM c1 FROM DUAL CONNECT BY LEVEL <= 10;
CREATE TABLE t4 AS SELECT MOD (ROWNUM, 10) + 100 c1 FROM DUAL CONNECT BY LEVEL <= 100;
CREATE TABLE t5 AS SELECT MOD (ROWNUM, 10) c1, RPAD ('X', 30) filler FROM DUAL CONNECT BY LEVEL <= 10000;
CREATE INDEX t5_i1 ON t5 (c1);
--分析表。
2.测试1：
SCOTT@book> alter session set statistics_level=all;
Session altered.
SCOTT@book> SELECT COUNT (*) FROM t3, t5 WHERE t3.c1 = t5.c1 AND t3.c1 = 1;
COUNT(*)
----------
1000
SCOTT@book> @&r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID dk73qsratggkh, child number 0
-------------------------------------
SELECT COUNT (*) FROM t3, t5 WHERE t3.c1 = t5.c1 AND t3.c1 = 1
Plan hash value: 1275968336
----------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 5 (100)| | 1 |00:00:00.01 | 6 | | | |
| 1 | SORT AGGREGATE | | 1 | 1 | 6 | | | 1 |00:00:00.01 | 6 | | | |
| 2 | MERGE JOIN CARTESIAN| | 1 | 1000 | 6000 | 5 (0)| 00:00:01 | 1000 |00:00:00.01 | 6 | | | |
|* 3 | TABLE ACCESS FULL | T3 | 1 | 1 | 3 | 3 (0)| 00:00:01 | 1 |00:00:00.01 | 2 | | | |
| 4 | BUFFER SORT | | 1 | 1000 | 3000 | 2 (0)| 00:00:01 | 1000 |00:00:00.01 | 4 | 73728 | 73728 | |
|* 5 | INDEX RANGE SCAN | T5_I1 | 1 | 1000 | 3000 | 2 (0)| 00:00:01 | 1000 |00:00:00.01 | 4 | | | |
----------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
3 - SEL$1 / T3@SEL$1
5 - SEL$1 / T5@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("T3"."C1"=1)
5 - access("T5"."C1"=1)
--可以发现ID=3,5的access或者filter是C1=1.而且取消了连接条件，变成了CARTESIAN集。
3.测试2：
SCOTT@book> SELECT * FROM t3, t4, t5 WHERE t3.c1 = t4.c1 AND t4.c1 = t5.c1;
no rows selected
SCOTT@book> @&r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID bd3j0xbhyq4yx, child number 0
-------------------------------------
SELECT * FROM t3, t4, t5 WHERE t3.c1 = t4.c1 AND t4.c1 = t5.c1
Plan hash value: 3251999038
-----------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 7 (100)| | 0 |00:00:00.01 | 4 | | | |
| 1 | NESTED LOOPS | | 1 | 1 | 41 | 7 (0)| 00:00:01 | 0 |00:00:00.01 | 4 | | | |
| 2 | NESTED LOOPS | | 1 | 1000 | 41 | 7 (0)| 00:00:01 | 0 |00:00:00.01 | 4 | | | |
|* 3 | HASH JOIN | | 1 | 1 | 7 | 6 (0)| 00:00:01 | 0 |00:00:00.01 | 4 | 2440K| 2440K| 1313K (0)|
| 4 | TABLE ACCESS FULL | T3 | 1 | 10 | 30 | 3 (0)| 00:00:01 | 10 |00:00:00.01 | 2 | | | |
| 5 | TABLE ACCESS FULL | T4 | 1 | 100 | 400 | 3 (0)| 00:00:01 | 100 |00:00:00.01 | 2 | | | |
|* 6 | INDEX RANGE SCAN | T5_I1 | 0 | 1000 | | 1 (0)| 00:00:01 | 0 |00:00:00.01 | 0 | | | |
| 7 | TABLE ACCESS BY INDEX ROWID| T5 | 0 | 1 | 34 | 1 (0)| 00:00:01 | 0 |00:00:00.01 | 0 | | | |
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
4 - SEL$1 / T3@SEL$1
5 - SEL$1 / T4@SEL$1
6 - SEL$1 / T5@SEL$1
7 - SEL$1 / T5@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("T3"."C1"="T4"."C1")
6 - access("T4"."C1"="T5"."C1")
--如果执行如下语句是等价的： SELECT * FROM t3, t4, t5 WHERE t3.c1 = t5.c1 AND t4.c1 = t5.c1;
SCOTT@book> SELECT * FROM t3, t4, t5 WHERE t3.c1 = t5.c1 AND t4.c1 = t5.c1;
no rows selected
SCOTT@book> @&r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID g5007pk488f76, child number 0
-------------------------------------
SELECT * FROM t3, t4, t5 WHERE t3.c1 = t5.c1 AND t4.c1 = t5.c1
Plan hash value: 1630033643
-------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 24 (100)| | 0 |00:00:00.01 | 58 | | | |
|* 1 | HASH JOIN | | 1 | 1 | 41 | 24 (0)| 00:00:01 | 0 |00:00:00.01 | 58 | 1021K| 1021K| 159K (0)|
|* 2 | HASH JOIN | | 1 | 1 | 38 | 21 (0)| 00:00:01 | 0 |00:00:00.01 | 58 | 2440K| 2440K| 1230K (0)|
| 3 | TABLE ACCESS FULL| T4 | 1 | 100 | 400 | 3 (0)| 00:00:01 | 100 |00:00:00.01 | 2 | | | |
| 4 | TABLE ACCESS FULL| T5 | 1 | 10000 | 332K| 18 (0)| 00:00:01 | 10000 |00:00:00.01 | 56 | | | |
| 5 | TABLE ACCESS FULL | T3 | 0 | 10 | 30 | 3 (0)| 00:00:01 | 0 |00:00:00.01 | 0 | | | |
-------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
3 - SEL$1 / T4@SEL$1
4 - SEL$1 / T5@SEL$1
5 - SEL$1 / T3@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("T3"."C1"="T5"."C1")
2 - access("T4"."C1"="T5"."C1")
--对比上下执行计划发生了很大变化，连接顺序发生了变化。
4.测试3：
--如果要达到测试1的效果，使用提示：
SELECT /*+ leading(t3 t4 t5) use_hash(t4) use_nl(t5) */ * FROM t3, t4, t5 WHERE t3.c1 = t5.c1 AND t4.c1 = t5.c1;
SCOTT@book> SELECT /*+ leading(t3 t4 t5) use_hash(t4) use_nl(t5) */ * FROM t3, t4, t5 WHERE t3.c1 = t5.c1 AND t4.c1 = t5.c1;
no rows selected
Plan hash value: 3284867853
-----------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 1015 (100)| | 0 |00:00:00.01 | 12 | | | |
| 1 | NESTED LOOPS | | 1 | 1 | 41 | 1015 (0)| 00:00:13 | 0 |00:00:00.01 | 12 | | | |
| 2 | NESTED LOOPS | | 1 | 100K| 41 | 1015 (0)| 00:00:13 | 0 |00:00:00.01 | 12 | | | |
| 3 | MERGE JOIN CARTESIAN | | 1 | 1000 | 7000 | 15 (0)| 00:00:01 | 1000 |00:00:00.01 | 4 | | | |
| 4 | TABLE ACCESS FULL | T3 | 1 | 10 | 30 | 3 (0)| 00:00:01 | 10 |00:00:00.01 | 2 | | | |
| 5 | BUFFER SORT | | 10 | 100 | 400 | 12 (0)| 00:00:01 | 1000 |00:00:00.01 | 2 | 4096 | 4096 | 4096 (0)|
| 6 | TABLE ACCESS FULL | T4 | 1 | 100 | 400 | 1 (0)| 00:00:01 | 100 |00:00:00.01 | 2 | | | |
|* 7 | INDEX RANGE SCAN | T5_I1 | 1000 | 100 | | 1 (0)| 00:00:01 | 0 |00:00:00.01 | 8 | | | |
| 8 | TABLE ACCESS BY INDEX ROWID| T5 | 0 | 1 | 34 | 1 (0)| 00:00:01 | 0 |00:00:00.01 | 0 | | | |
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
4 - SEL$1 / T3@SEL$1
6 - SEL$1 / T4@SEL$1
7 - SEL$1 / T5@SEL$1
8 - SEL$1 / T5@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
7 - access("T4"."C1"="T5"."C1")
filter("T3"."C1"="T5"."C1")
--实际上并没有实现上面的执行计划，而是产生了CARTESIAN集合。必须要加入t3.c1=t4.c1条件。
SCOTT@book> SELECT /*+ leading(t3 t4 t5) use_hash(t4) use_nl(t5) */ * FROM t3, t4, t5 WHERE t3.c1 = t5.c1 AND t4.c1 = t5.c1 and t3.c1=t4.c1;
no rows selected
SCOTT@book> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID 9nzh9uxm6b11z, child number 0
-------------------------------------
SELECT /*+ leading(t3 t4 t5) use_hash(t4) use_nl(t5) */ * FROM t3, t4,
t5 WHERE t3.c1 = t5.c1 AND t4.c1 = t5.c1 and t3.c1=t4.c1
Plan hash value: 3251999038
-----------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 7 (100)| | 0 |00:00:00.01 | 4 | | | |
| 1 | NESTED LOOPS | | 1 | 1 | 41 | 7 (0)| 00:00:01 | 0 |00:00:00.01 | 4 | | | |
| 2 | NESTED LOOPS | | 1 | 100 | 41 | 7 (0)| 00:00:01 | 0 |00:00:00.01 | 4 | | | |
|* 3 | HASH JOIN | | 1 | 1 | 7 | 6 (0)| 00:00:01 | 0 |00:00:00.01 | 4 | 2440K| 2440K| 1333K (0)|
| 4 | TABLE ACCESS FULL | T3 | 1 | 10 | 30 | 3 (0)| 00:00:01 | 10 |00:00:00.01 | 2 | | | |
| 5 | TABLE ACCESS FULL | T4 | 1 | 100 | 400 | 3 (0)| 00:00:01 | 100 |00:00:00.01 | 2 | | | |
|* 6 | INDEX RANGE SCAN | T5_I1 | 0 | 100 | | 1 (0)| 00:00:01 | 0 |00:00:00.01 | 0 | | | |
| 7 | TABLE ACCESS BY INDEX ROWID| T5 | 0 | 1 | 34 | 1 (0)| 00:00:01 | 0 |00:00:00.01 | 0 | | | |
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
4 - SEL$1 / T3@SEL$1
5 - SEL$1 / T4@SEL$1
6 - SEL$1 / T5@SEL$1
7 - SEL$1 / T5@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("T3"."C1"="T4"."C1")
6 - access("T4"."C1"="T5"."C1")
filter("T3"."C1"="T5"."C1")
--看来以后在优化多表连接sql语句时适当加入多余的条件看看执行计划是否存在变化。也说明oracle的优化器还有许多需要改进的地方。