[20180612]函数与标量子查询10.txt
--//前面看http://www.cnblogs.com/kerrycode/p/9099507.html链接,里面提到:
通俗来将，当使用标量子查询的时候，ORACLE会将子查询结果缓存在哈希表中， 如果后续的记录出现同样的值，优化器通过缓存在哈希
表中的值，判断重复值不用重复调用函数，直接使用上次计算结果即可。从而减少调用函数次数，从而达到优化性能的效果。另外在
ORACLE 10和11中， 哈希表只包含了255个Buckets，也就是说它能存储255个不同值，如果超过这个范围，就会出现散列冲突，那些出现
散列冲突的值就会重复调用函数，即便如此，依然能达到大幅改善性能的效果。
--//前几天测试11.2.0.4 for linux下,哈希表不止255个Buckets.
--//另外也测试再10g下到底有512个Buckets.今天测试11g是多少,我感觉11g应该是2048,这意味着测试数据量可能需要很大,我原来的测试
--//方法需要的时间更长.
1.环境:
SYS@test> @ &r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- ----------------------------------------------------------------
x86_64/Linux 2.4.xx 10.2.0.4.0 Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
grant execute on sys.dbms_lock to scott;
CREATE OR REPLACE FUNCTION sleep1 (seconds IN NUMBER)
RETURN NUMBER
is
d_date date;
BEGIN
select sysdate into d_date from dual;
sys.dbms_lock.sleep(seconds/10);
RETURN seconds;
END;
/
CREATE OR REPLACE FUNCTION sleep (seconds IN NUMBER)
RETURN NUMBER
is
d_date date;
BEGIN
select sysdate into d_date from dual;
--//sys.dbms_lock.sleep(0.01);
RETURN seconds;
END;
/
create table t as select rownum id1,mod(rownum-1,20000)+1 id2 from dual connect by level<=40000;
--//ALTER TABLE t MINIMIZE RECORDS_PER_BLOCK ;
--//注意插入数据的顺序,我以前的插入有1点问题,导致id2显示不按照1-20000,1-20000显示(执行select * from t).
--//导致测试出现一些奇怪情况.
--//分析表略.
2.测试:
--//建立脚本by.txt:
set term off
alter session set statistics_level=all;
variable x number;
exec :x := &&1;
select t.*,(select sleep(id2) from dual) s from t where id2<=:x;
set term on
@ &r/dpc '' ''
quit
--//建立shell脚本by.sh:
#! /bin/bash
# rm -f ez.txt
for i in $(seq 20000)
do
sqlplus -s -l scott/book @by.txt $i >> ez.txt
done
--//这样执行脚本就ok了.
--//取出数字
$ egrep 'FAST DUAL' ez.txt | cut -f5 -d"|" > e2.txt
$ egrep 'SELECT STATEMENT' ez.txt | cut -f10 -d"|" > e3.txt
$ paste e2.txt e3.txt -d"," > e4.txt
SCOTT@book> create table t1 ( a number ,b number);
Table created.
--//注:a表示执行fast dual次数,也就是递归次数.b表示查询记录数量,
--//修改e4.txt ,改写成inert插入表t1.执行如下:
:%s/^/insert into t1 values(/g
:%s/$/);/g
select max(id2) from (
SELECT id2, r, rp
FROM ( SELECT b / 2 id2, a r, LAG (a) OVER (ORDER BY b) rp
FROM t1
ORDER BY b/2)
WHERE r - rp = 1 order by id2);
MAX(ID2)
----------
9234
--//9234还会进入backupset,后面的数字带入都是出现hash 冲突的情况.没想到这么小,这样估计不是2048个buckets.
SELECT id2, r, rp
FROM ( SELECT b / 2 id2, a r, LAG (a) OVER (ORDER BY b) rp
FROM t1
ORDER BY b/2)
WHERE r - rp >= 2 and id2<=9234 ;
--//输出太长,一共8210个值,略,这个结果就是在1-9234之间,出现hash冲突的值.
select count(*) from
(SELECT id2, r, rp
FROM ( SELECT b / 2 id2, a r, LAG (a) OVER (ORDER BY b) rp
FROM t1
ORDER BY b/2)
WHERE r - rp >= 2 and id2<=9234 );
COUNT(*)
----------
8210
--// 9234-8210 = 1024 ,可以看出11.2.0.4标量子查询的哈希表大小是1024个buckets.
select rowid,t.*,(select sleep(id2) from dual) s from t where id2<=9234
and id2 not in
(
SELECT /*+ NL_AJ */ id2
FROM ( SELECT b / 2 id2, a r, LAG (a) OVER (ORDER BY b) rp
FROM t1
ORDER BY b/2)
WHERE r - rp >= 2 and id2<=9234
);
SCOTT@book> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID fpd89t0b5dzc8, child number 0
-------------------------------------
select rowid,t.*,(select sleep(id2) from dual) s from t where
id2<=9234 and id2 not in ( SELECT /*+ NL_AJ */ id2 FROM ( SELECT b /
2 id2, a r, LAG (a) OVER (ORDER BY b) rp FROM t1
ORDER BY b/2) WHERE r - rp >= 2 and id2<=9234 )
Plan hash value: 4130365942
---------------------------------------------------------------------------------------------------------------------------------------------------
| 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 | | | 291K(100)| | 2048 |00:00:47.55 | 138 | | | |
| 1 | FAST DUAL | | 1024 | 1 | | 2 (0)| 00:00:01 | 1024 |00:00:00.01 | 0 | | | |
| 2 | NESTED LOOPS ANTI | | 1 | 18468 | 865K| 291K (18)| 00:58:22 | 2048 |00:00:47.55 | 138 | | | |
|* 3 | TABLE ACCESS FULL | T | 1 | 18469 | 162K| 25 (0)| 00:00:01 | 18468 |00:00:00.01 | 93 | | | |
|* 4 | VIEW | | 18468 | 1 | 39 | 16 (19)| 00:00:01 | 16420 |00:00:47.53 | 45 | | | |
| 5 | SORT ORDER BY | | 18468 | 20000 | 195K| 16 (19)| 00:00:01 | 40M|00:00:44.63 | 45 | 761K| 499K| 676K (0)|
| 6 | WINDOW SORT | | 2048 | 20000 | 195K| 16 (19)| 00:00:01 | 40M|00:00:30.57 | 45 | 761K| 499K| 676K (0)|
| 7 | TABLE ACCESS FULL| T1 | 1 | 20000 | 195K| 13 (0)| 00:00:01 | 20000 |00:00:00.01 | 45 | | | |
---------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$2 / DUAL@SEL$2
2 - SEL$8771BF6C
3 - SEL$8771BF6C / T@SEL$1
4 - SEL$4 / from$_subquery$_003@SEL$3
5 - SEL$4
7 - SEL$4 / T1@SEL$4
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("ID2"<=9234)
4 - filter(("ID2"="ID2" AND "R"-"RP">=2 AND "ID2"<=9234))
--//正好1024,说明11.2.0.4,哈希表只包含了1024个Buckets，也就是说它能存储1024个不同值，
--//删除冲突的记录看看.
delete from t where id2 in (SELECT id2
FROM ( SELECT b / 2 id2, a r, LAG (a) OVER (ORDER BY b) rp
FROM t1
ORDER BY b/2)
WHERE r - rp >= 2 and id2<=9234 );
16420 rows deleted.
SCOTT@book> commit ;
Commit complete.
select t.*,(select sleep(id2) from dual) s from t where id2<=9234;
SCOTT@book> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID 7g5wrr9a7g7v8, child number 0
-------------------------------------
select t.*,(select sleep(id2) from dual) s from t where id2<=9234
Plan hash value: 1032660217
--------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 25 (100)| | 2048 |00:00:00.01 | 93 |
| 1 | FAST DUAL | | 1024 | 1 | | 2 (0)| 00:00:01 | 1024 |00:00:00.01 | 0 |
|* 2 | TABLE ACCESS FULL| T | 1 | 18469 | 162K| 25 (0)| 00:00:01 | 2048 |00:00:00.01 | 93 |
--------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$2 / DUAL@SEL$2
2 - SEL$1 / T@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("ID2"<=9234)
--//这样如果
select rowid,t.*,(select sleep(id2) from dual) s from t where (id2<=9234 ) or id2=:x;
--//:x 选择 9235-20000 任何一个 ,fast dual 的starts都是1026,也就是存在冲突.大家可以自行验证.
--//dpc脚本如下:
set verify off
select * from table(dbms_xplan.display_cursor(NVL('&1',NULL),NULL,'ALL ALLSTATS LAST PEEKED_BINDS cost partition -projection -outline &2'));
prompt
prompt argment : typical all advanced partition predicate remote note parallel projection alias peeked_binds outline adaptive
prompt
