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2019-01-02
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摘要：本篇教程探讨了Oracle数据库入门之使用提示OR_EXPAND优化，希望阅读本篇文章以后大家有所收获，帮助大家对相关内容的理解更加深入。
本篇教程探讨了Oracle数据库入门之使用提示OR_EXPAND优化，希望阅读本篇文章以后大家有所收获，帮助大家对相关内容的理解更加深入。
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1.环境:
SCOTT@test01p> @ ver1
PORT_STRING VERSION BANNER CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0 12.2.0.1.0 Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production 0
create table t1 as select rownum id1 ,rownum id2 ,lpad('x',100,'x') name from dual connect by level<=6000;
create table t2 as select rownum id1 ,rownum id2 ,lpad('x',100,'x') name from dual connect by level<=6000;
create index i_t1_id1 on t1(id1);
create index i_t1_id2 on t1(id2);
create index i_t2_id1 on t2(id1);
--//分析略.
2.测试:
SCOTT@test01p> alter session set statistics_level = all;
Session altered.
SCOTT@test01p> select * from t1 where t1.id1 in (select t2.id1 from t2 where t2.id1=11 ) or (t1.id2=10 );
ID1 ID2 NAME
---------- ---------- ----------------------------------------------------------------------------------------------------
10 10 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
11 11 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
SCOTT@test01p> @ dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID gz5pqkg6svm7k, child number 0
-------------------------------------
select * from t1 where t1.id1 in (select t2.id1 from t2 where
t2.id1=11 ) or (t1.id2=10 )
Plan hash value: 1962644737
-------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 30 (100)| | 2 |00:00:00.01 | 115 |
|* 1 | FILTER | | 1 | | | | | 2 |00:00:00.01 | 115 |
| 2 | TABLE ACCESS FULL| T1 | 1 | 6000 | 638K| 30 (0)| 00:00:01 | 6000 |00:00:00.01 | 113 |
|* 3 | FILTER | | 5999 | | | | | 1 |00:00:00.01 | 2 |
|* 4 | INDEX RANGE SCAN| I_T2_ID1 | 1 | 1 | 4 | 1 (0)| 00:00:01 | 1 |00:00:00.01 | 2 |
-------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
2 - SEL$1 / T1@SEL$1
3 - SEL$2
4 - SEL$2 / T2@SEL$2
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("T1"."ID2"=10 OR IS NOT NULL))
3 - filter(11=:B1)
4 - access("T2"."ID1"=:B1)
32 rows selected.
--//执行计划存在1个全表扫描.里面的索引选择性很好,oracle并没有选择合理的执行计划.
--//而且有1个小小的细节,id=4的starts=1,而前面的id=3的starts=5999.你可以看出这里oracle显示执行计划有1个小小的bug.
--//id=4的starts应该是5999.这样看到的逻辑读不应该是后面的2而是2*5999 = 11998.
--//而且你可以看出oracle忽略的id=4多次INDEX RANGE SCAN的成本.
--//链接//www.itpub.net/thread-2107240-2-1.html里面的显示倒是正确的.它的版本是11.2.0.4.180717.
3.是否通过提示优化sql语句:
--//首先想到的是USE_CONCAT.
select /*+ USE_CONCAT(@"SEL$1" 8 OR_PREDICATES(1)) */ * from t1 where t1.id1 in (select /*+unnest */ t2.id1 from t2 where t2.id1=11 ) or (t1.id2=10 );
--//执行计划如下:
-------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 33 (100)| | 2 |00:00:00.01 | 118 |
| 1 | CONCATENATION | | 1 | | | | | 2 |00:00:00.01 | 118 |
| 2 | TABLE ACCESS BY INDEX ROWID BATCHED| T1 | 1 | 1 | 109 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 4 |
|* 3 | INDEX RANGE SCAN | I_T1_ID2 | 1 | 1 | | 1 (0)| 00:00:01 | 1 |00:00:00.01 | 3 |
|* 4 | FILTER | | 1 | | | | | 1 |00:00:00.01 | 114 |
|* 5 | TABLE ACCESS FULL | T1 | 1 | 5999 | 638K| 30 (0)| 00:00:01 | 5999 |00:00:00.01 | 112 |
|* 6 | FILTER | | 5999 | | | | | 1 |00:00:00.01 | 2 |
|* 7 | INDEX RANGE SCAN | I_T2_ID1 | 1 | 1 | 4 | 1 (0)| 00:00:01 | 1 |00:00:00.01 | 2 |
-------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
2 - SEL$1_1 / T1@SEL$1
3 - SEL$1_1 / T1@SEL$1
5 - SEL$1_2 / T1@SEL$1_2
6 - SEL$2
7 - SEL$2 / T2@SEL$2
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("T1"."ID2"=10)
4 - filter( IS NOT NULL)
5 - filter(LNNVL("T1"."ID2"=10))
6 - filter(11=:B1)
7 - access("T2"."ID1"=:B1)
--//很奇怪id=4,依旧选择过滤,unnest提示没有用.实际上使用USE_CONCAT相当每个or分支加入LNNVL(条件)来排他符合条件的记录.
--//也就是oracle依旧选择的执行计划不是很理想,甚至比前面还要差.
4.尝试OR_EXPAND提示:
select /*+ OR_EXPAND */ * from t1 where t1.id1 in (select /*+ unnest */ t2.id1 from t2 where t2.id1=11 ) or (t1.id2=10 );
--//执行计划如下:
Plan hash value: 1716482303
----------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
----------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 5 (100)| | 2 |00:00:00.01 | 9 |
| 1 | VIEW | VW_ORE_BA8ECEFB | 1 | 2 | 156 | 5 (0)| 00:00:01 | 2 |00:00:00.01 | 9 |
| 2 | UNION-ALL | | 1 | | | | | 2 |00:00:00.01 | 9 |
| 3 | TABLE ACCESS BY INDEX ROWID BATCHED | T1 | 1 | 1 | 109 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 4 |
|* 4 | INDEX RANGE SCAN | I_T1_ID2 | 1 | 1 | | 1 (0)| 00:00:01 | 1 |00:00:00.01 | 3 |
| 5 | NESTED LOOPS SEMI | | 1 | 1 | 113 | 3 (0)| 00:00:01 | 1 |00:00:00.01 | 5 |
|* 6 | TABLE ACCESS BY INDEX ROWID BATCHED| T1 | 1 | 1 | 109 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 3 |
|* 7 | INDEX RANGE SCAN | I_T1_ID1 | 1 | 1 | | 1 (0)| 00:00:01 | 1 |00:00:00.01 | 2 |
|* 8 | INDEX RANGE SCAN | I_T2_ID1 | 1 | 1 | 4 | 1 (0)| 00:00:01 | 1 |00:00:00.01 | 2 |
----------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SET$9162BF3C / VW_ORE_BA8ECEFB@SEL$BA8ECEFB
2 - SET$9162BF3C
3 - SET$9162BF3C_1 / T1@SEL$1
4 - SET$9162BF3C_1 / T1@SEL$1
5 - SEL$C90BA1D5
6 - SEL$C90BA1D5 / T1@SEL$1
7 - SEL$C90BA1D5 / T1@SEL$1
8 - SEL$C90BA1D5 / T2@SEL$2
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('12.2.0.1')
DB_VERSION('12.2.0.1')
ALL_ROWS
OUTLINE_LEAF(@"SEL$C90BA1D5")
UNNEST(@"SEL$2")
OUTLINE_LEAF(@"SET$9162BF3C_1")
OUTLINE_LEAF(@"SET$9162BF3C")
OR_EXPAND(@"SEL$1" (1) (2))
OUTLINE_LEAF(@"SEL$BA8ECEFB")
OUTLINE(@"SET$9162BF3C_2")
OUTLINE(@"SEL$2")
OUTLINE(@"SET$9162BF3C")
OR_EXPAND(@"SEL$1" (1) (2))
OUTLINE(@"SEL$1")
NO_ACCESS(@"SEL$BA8ECEFB" "VW_ORE_BA8ECEFB"@"SEL$BA8ECEFB")
INDEX_RS_ASC(@"SET$9162BF3C_1" "T1"@"SEL$1" ("T1"."ID2"))
BATCH_TABLE_ACCESS_BY_ROWID(@"SET$9162BF3C_1" "T1"@"SEL$1")
INDEX_RS_ASC(@"SEL$C90BA1D5" "T1"@"SEL$1" ("T1"."ID1"))
BATCH_TABLE_ACCESS_BY_ROWID(@"SEL$C90BA1D5" "T1"@"SEL$1")
INDEX(@"SEL$C90BA1D5" "T2"@"SEL$2" ("T2"."ID1"))
LEADING(@"SEL$C90BA1D5" "T1"@"SEL$1" "T2"@"SEL$2")
USE_NL(@"SEL$C90BA1D5" "T2"@"SEL$2")
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("T1"."ID2"=10)
6 - filter(LNNVL("T1"."ID2"=10))
7 - access("T1"."ID1"=11)
8 - access("T2"."ID1"=11)
filter("T1"."ID1"="T2"."ID1")
--//12c下oracle选择正确的执行计划.可以发现id=2使用UNION-ALL,也就是oracle做了查询转换成union all的形式.
--//另外我曾经尝试将ounline date的提示信息加入到11g环境,执行计划依旧没有选择OR_EXPAND.
--//通过10053事件看看.
SCOTT@test01p> @ 10053x cg5kmfhgczjfd 0
PL/SQL procedure successfully completed.
ORE: after OR Expansion:******* UNPARSED QUERY IS *******
SELECT "VW_ORE_BA8ECEFB"."ITEM_1" "ID1","VW_ORE_BA8ECEFB"."ITEM_2" "ID2","VW_ORE_BA8ECEFB"."ITEM_3" "NAME" FROM ( (SELECT "T1"."ID1" "ITEM_1","T1"."ID2" "ITEM_2","T1"."NAME" "ITEM_3" FROM "SCOTT"."T1" "T1" WHERE "T1"."ID2"=10) UNION ALL (SELECT "T1"."ID1" "ITEM_1","T1"."ID2" "ITEM_2","T1"."NAME" "ITEM_3" FROM "SCOTT"."T1" "T1" WHERE "T1"."ID1"=ANY (SELECT /*+ UNNEST */ "T2"."ID1" "ID1" FROM "SCOTT"."T2" "T2" WHERE "T2"."ID1"=11) AND LNNVL("T1"."ID2"=10))) "VW_ORE_BA8ECEFB"
--//格式化显示如下:
SELECT "VW_ORE_BA8ECEFB"."ITEM_1" "ID1"
,"VW_ORE_BA8ECEFB"."ITEM_2" "ID2"
,"VW_ORE_BA8ECEFB"."ITEM_3" "NAME"
FROM ( (SELECT "T1"."ID1" "ITEM_1"
,"T1"."ID2" "ITEM_2"
,"T1"."NAME" "ITEM_3"
FROM "SCOTT"."T1" "T1"
WHERE "T1"."ID2" = 10)
UNION ALL
(SELECT "T1"."ID1" "ITEM_1"
,"T1"."ID2" "ITEM_2"
,"T1"."NAME" "ITEM_3"
FROM "SCOTT"."T1" "T1"
WHERE "T1"."ID1" = ANY (SELECT /*+ UNNEST */
"T2"."ID1" "ID1"
FROM "SCOTT"."T2" "T2"
WHERE "T2"."ID1" = 11)
AND LNNVL ("T1"."ID2" = 10))) "VW_ORE_BA8ECEFB";
--//也就是oracle查询转换为 UNION ALL的形式.
--//你可以看到第2个条件人为的加入LNNVL ("T1"."ID2" = 10).
--// OR_EXPAND 提示 与 USE_CONCAT 提示到底有什么不同?
5.补充使用USE_CONCAT看到的情况:
select /*+ USE_CONCAT(@"SEL$1" 8 OR_PREDICATES(1)) */ * from t1 where t1.id1 in (select /*+unnest */ t2.id1 from t2 where t2.id1=11 ) or (t1.id2=10 );
SCOTT@test01p> @ 10053x 18h6hkqcqq3w2 0
PL/SQL procedure successfully completed.
--//看这些太烦,不过可以发现如下:
LORE: Or-Expansion validity checks failed on query block SEL$2 (#2) because Cost based OR expansion enabled
SYS@test01p> @ hide or_exp
old 10: and lower(a.ksppinm) like lower('%&1%')
new 10: and lower(a.ksppinm) like lower('%or_exp%')
NAME DESCRIPTION DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE
---------------------------------- ------------------------------------------------- ------------- ------------- ------------
_no_or_expansion OR expansion during optimization disabled TRUE FALSE FALSE
_optimizer_cbqt_or_expansion enables cost based OR expansion TRUE ON ON
_optimizer_interleave_or_expansion interleave OR Expansion during CBQT TRUE TRUE TRUE
_optimizer_or_expansion control or expansion approach used TRUE DEPTH DEPTH
_optimizer_or_expansion_subheap Use subheap for optimizer or-expansion TRUE TRUE TRUE
_or_expand_nvl_predicate enable OR expanded plan for NVL/DECODE predicate TRUE TRUE TRUE
6 rows selected.
--//也就是12c缺省打开因为以上原因.不过我尝试"_optimizer_cbqt_or_expansion"=off也无效.放弃!!
--//我也尝试提高全表扫描的成本看看是否执行计划会发生改变,不过依旧没用.
SCOTT@test01p> exec dbms_stats.SET_TABLE_STATS(user,'T1',NUMBLKS=>800000000000);
PL/SQL procedure successfully completed.
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