本篇文章为大家展示了怎么理解v$sql的exact_matching_signature与force_matching_signature.txt,内容简明扼要并且容易理解,绝对能使你眼前一亮,通过这篇文章的详细介绍希望你能有所收获。
[20120918]理解v$sql的exact_matching_signature与force_matching_signature.txt
理解v$sql的exact_matching_signature与force_matching_signature,对于使用sql profile以及SPM有重要意义,自己对于这个一直没有很好的理解,
今天做一个测试看看,可能不全面^_^.
SQL> select * from v$version ;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
1.建立测试例子:
create table t as select rownum id1,trunc((rownum-1)/10)+1 id2,'test' name from dual connect by level<=100;
create index i_t_id1 on t(id1);
alter system flush shared_pool;
select /*+ findme */ name from t where id1=42;
select /*+ findme1 */ name from t where id1=42;
select /*+ findme */ Name from t where id1=42;
SELECT /*+ findme */ nAme FROM t WHERE id1 = 42;
SELECT /*+ Findme */ nAme FROM T WHERE id1 = 42 ;
SELECT /*+ Findme test */ nAme FROM T WHERE id1 = 42 ;
SELECT /*+ full(t) Findme */ nAme FROM T WHERE id1 = 42 ;
SELECT /*+ index(t) Findme */ nAme FROM T WHERE id1 = 42 ;
column format r 99
column sql_text format a60
column force_matching_signature format 99999999999999999999
column exact_matching_signature format 99999999999999999999
select rownum r,x.* from (
select sql_id,plan_hash_value,sql_text,exact_matching_signature,force_matching_signature
from v$sql where lower(sql_text) like '%/*%findme%' and sql_text not like '%v$sql%' order by exact_matching_signature) x;
R SQL_ID PLAN_HASH_VALUE SQL_TEXT EXACT_MATCHING_SIGNATURE FORCE_MATCHING_SIGNATURE
1 0m8m91zz80rvh 1183254286 SELECT /*+ index(t) Findme */ nAme FROM T WHERE id1 = 42 1611223796141114091 11078870919385499790
2 f7aadcsrf2kkp 1601196873 SELECT /*+ full(t) Findme */ nAme FROM T WHERE id1 = 42 2823236535463672246 17243933052976400209
3 dhfmwm002g4z4 1183254286 SELECT /*+ Findme */ nAme FROM T WHERE id1 = 42 4375557158775460903 698688741679991361
4 85t7vsqqgjpst 1183254286 select /*+ findme */ name from t where id1=42 4375557158775460903 698688741679991361
5 5bcck0z12q1g6 1183254286 SELECT /*+ findme */ nAme FROM t WHERE id1 = 42 4375557158775460903 698688741679991361
6 7vbndspk1kt83 1183254286 select /*+ findme */ Name from t where id1=42 4375557158775460903 698688741679991361
7 2d7cgsth617gy 1183254286 SELECT /*+ Findme test */ nAme FROM T WHERE id1 = 42 6656879127321462824 2920394029241435021
8 apv57y4bk2uqv 1183254286 select /*+ findme1 */ name from t where id1=42 14445306118291341866 11192650436549747287
8 rows selected.
-- 仔细观察,可以发现:
1.EXACT_MATCHING_SIGNATURE 一样的,比如3,4,5,6 EXACT_MATCHING_SIGNATURE=4375557158775460903,其对应的FORCE_MATCHING_SIGNATURE也一样(698688741679991361).
2.如果注解仅仅是大小写的问题,其EXACT_MATCHING_SIGNATURE也是一样的,其他空格大小写也不受影响.
3.如果有注解不同,其EXACT_MATCHING_SIGNATURE就不同了.
我的感觉就是把语句换成大写,注解部分也是换成大写,去除多余的空格等字符,算出一个东西.
这个东西很容易联想oracle的一个参数cursor_sharing.
exect=>表示精确匹配
force=>估计就是绑定以后匹配的.
alter system flush shared_pool;
select /*+ findme */ name from t where id1= 42;
select /*+ Findme */ name from t where id1= 43;
SQL> @a
R SQL_ID PLAN_HASH_VALUE SQL_TEXT EXACT_MATCHING_SIGNATURE FORCE_MATCHING_SIGNATURE
1 373zfvx9h7xah 1183254286 select /*+ findme */ name from t where id1= 42 4375557158775460903 698688741679991361
2 5nyk32fjxxqkc 1183254286 select /*+ Findme */ name from t where id1= 43 7094585129451441419 698688741679991361
--想象把常量换成了变量,这里的FORCE_MATCHING_SIGNATURE一样.
SQL> alter system flush shared_pool;
SQL> variable v_id1 number ;
SQL> variable v_idx number ;
SQL> exec :v_id1 := 42 ;
SQL> exec :v_idx := 43 ;
SQL> select /*+ Findme */ name from t where id1= :v_id1 and id2=1;
SQL> select /*+ Findme */ name from t where id1= :v_id1 and id2=2;
SQL> @a
R SQL_ID PLAN_HASH_VALUE SQL_TEXT EXACT_MATCHING_SIGNATURE FORCE_MATCHING_SIGNATURE
1 b3x2pcgkxaxft 1183254286 select /*+ Findme */ name from t where id1= :v_id1 and id2=2 7008393373276421720 7008393373276421720
2 ckr7rh2zfrwcv 1183254286 select /*+ Findme */ name from t where id1= :v_id1 and id2=1 14799038700516685754 14799038700516685754
--但是如果语句中存在绑定变量,这个又不一样.而且这个时候EXACT_MATCHING_SIGNATURE = FORCE_MATCHING_SIGNATURE.
--有点乱,google找到一篇文章,老熊总结的,转抄如下.
http://www.laoxiong.net/sql-profiles-part.html
对SQL语句,去掉重复的空格(不包括字符常量),将大小写转换成相同,比如均为大写(不包括字符常量)后,如果
SQL相同,那么SQL语句的exact_matching_signature就是相同的。对SQL语句,去掉重复的空格(不包括字符常量),将大小写转换成相同,
比如均为大写(不包括字符常量),然后去掉SQL中的常量,如果SQL相同,那么SQL语句的force_matching_signature就是相同的。但是例
外的情况是:如果SQL中有绑定变量,force_matching_signature就会与exact_matching_signature一样的生成标准。
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原创文章,作者:Maggie-Hunter,如若转载,请注明出处:https://blog.ytso.com/200115.html