本篇内容主要讲解“ACS与PL/SQL的工作情况分析”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“ACS与PL/SQL的工作情况分析”吧!

ACS与PL/SQL

我们来看下ACS在PL/SQL里的工作情况，结果可能会令你非常失望。

首先构造一个PL/SQL，里面使用到了我们在本章中创建的表T：

SQL>varsql_idvarchar2(255)

SQL>altersystemflushshared_pool;


Systemaltered.

SQL>declare

2xinteger;

3nnumber;

4begin

5foriin1..10loop

6ifi=1then

7x:=500000;

8else

9x:=1;

10endif;

11selectcount(object_id)intonfromtwhereid>x;

12endloop;

13end;

14/


PL/SQLproceduresuccessfullycompleted.

这段PL/SQL首先会执行‘selectcount(object_id)intonfromtwhereid>100000’1次，然后会执行‘selectcount(object_id)intonfromtwhereid>1’9次，执行完成后，我们来看看是否会使用到ACS。

SQL>select

2sql_id

3,child_number

4,executions

5,parse_calls

6,buffer_gets

7,is_bind_sensitive

8,is_bind_aware

9from

10v$sql

11where

12sql_id='gp03v5aw085v3';


SQL_IDCHILD_NUMBEREXECUTIONSPARSE_CALLSBUFFER_GETSISIS

---------------------------------------------------------------

gp03v5aw085v30101646875YN


非常可惜，这个SQL并没有产生多个子游标，虽然已经识别到这个SQL为绑定敏感is_bind_sensitive='Y'，但是is_bind_aware='N'。

SQL>SELECThash_value,sql_id,child_number,bucket_id,COUNT

2FROMv$sql_cs_histogram

3WHEREsql_id='gp03v5aw085v3'

4ORDERBYsql_id,child_number;


HASH_VALUESQL_IDCHILD_NUMBERBUCKET_IDCOUNT

---------------------------------------------------------

3087275875gp03v5aw085v3001

3087275875gp03v5aw085v3029

3087275875gp03v5aw085v3010

虽然v$sql_cs_histogram已经监控到了处理行数的巨大改变，但是却没有生成新的游标。


SQL>select*fromtable(dbms_xplan.display_cursor(:sql_id,null,'+PEEKED_BINDS'));


PLAN_TABLE_OUTPUT

----------------------------------------------------------------------------------------

SQL_IDgp03v5aw085v3,childnumber0

-------------------------------------

SELECTCOUNT(OBJECT_ID)FROMTWHEREID>:B1


Planhashvalue:3694077449


-------------------------------------------------------------------------------------

|Id|Operation|Name|Rows|Bytes|Cost(%CPU)|Time|

-------------------------------------------------------------------------------------

|0|SELECTSTATEMENT||||4(100)||

|1|SORTAGGREGATE||1|10|||

|2|TABLEACCESSBYINDEXROWID|T|1|10|4(0)|00:00:01|

|*3|INDEXRANGESCAN|I|1||3(0)|00:00:01|

-------------------------------------------------------------------------------------


PeekedBinds(identifiedbyposition):

--------------------------------------


1-:B1(NUMBER):5000000


PredicateInformation(identifiedbyoperationid):

---------------------------------------------------


3-access("ID">:B1)

执行计划一直沿用的是第一次产生的执行计划，根据PeekedBinds(identifiedbyposition):的值为5000000可以推断出来。我们尝试在SQL里增加bind_awarehint看看，这个hint的作用在本章的最佳实践小节中介绍，这里不再赘述。

SQL>declare

2xinteger;

3nnumber;

4begin

5foriin1..10loop

6ifi=1then

7x:=5000000;

8else

9x:=1;

10endif;

11select/*+bind_aware*/count(object_id)intonfromtwhereid>x;

12endloop;

13end;

14/


PL/SQLproceduresuccessfullycompleted.


SQL>select

2sql_id

3,child_number

4,executions

5,parse_calls

6,buffer_gets

7,is_bind_sensitive

8,is_bind_aware

9from

10v$sql

11where

12sql_id='5542a2rzny69v';


SQL_IDCHILD_NUMBEREXECUTIONSPARSE_CALLSBUFFER_GETSISIS

---------------------------------------------------------------

5542a2rzny69v0101687396YY

虽然优化器已经标记这个游标is_bind_aware='Y'了，但是依然没有新的游标产生出来。在MOS上查找类似的问题，会发现一个BUG：
Bug8357294:ADAPTIVEcursorSHARINGDOESN'TWORKFORSTATICSQLcursorSFROMPL/SQL
标题的意思是由于BUG，ACS不能工作在PL/SQL的静态游标里。但是根据测试动态游标也不能工作。

SQL>declare

2xinteger;

3nnumber;

4begin

5foriin1..10loop

6ifi=1then

7x:=5000000;

8else

9x:=1;

10endif;

11executeimmediate

12'selectcount(object_id)fromtwhereid>:x'intonusingx;

13endloop;

14end;

15/


PL/SQLproceduresuccessfullycompleted.


SQL>select

2sql_id

3,child_number

4,executions

5,parse_calls

6,buffer_gets

7,is_bind_sensitive

8,is_bind_aware

9from

10v$sql

11where

12sql_id='6qwg6gauwbpm8';


SQL_IDCHILD_NUMBEREXECUTIONSPARSE_CALLSBUFFER_GETSISIS

---------------------------------------------------------------

6qwg6gauwbpm80101687580YN

文中提到了Session_Cached_Cursors在设置为0后，ACS就可以正常工作了，经过试验也如它所说。

SQL>altersessionsetSession_Cached_Cursors=0;


Sessionaltered.


SQL>altersystemflushshared_pool;


Systemaltered.


SQL>declare

2xinteger;

3nnumber;

4begin

5foriin1..10loop

6ifi=1then

7x:=5000000;

8else

9x:=1;

10endif;

11selectcount(object_id)intonfromtwhereid>x;

12endloop;

13end;

14/


PL/SQLproceduresuccessfullycompleted.


SQL>select

2sql_id

3,child_number

4,executions

5,parse_calls

6,buffer_gets

7,is_bind_sensitive

8,is_bind_aware

9from

10v$sql

11where

12sql_id='gp03v5aw085v3';


SQL_IDCHILD_NUMBEREXECUTIONSPARSE_CALLSBUFFER_GETSISIS

---------------------------------------------------------------

gp03v5aw085v302376405YN

gp03v5aw085v3187517480YY


SQL>select*fromtable(dbms_xplan.display_cursor('gp03v5aw085v3',null));


PLAN_TABLE_OUTPUT

-------------------------------------------------------------------------------------------

SQL_IDgp03v5aw085v3,childnumber0

-------------------------------------

SELECTCOUNT(OBJECT_ID)FROMTWHEREID>:B1


Planhashvalue:3694077449


-------------------------------------------------------------------------------------

|Id|Operation|Name|Rows|Bytes|Cost(%CPU)|Time|

-------------------------------------------------------------------------------------

|0|SELECTSTATEMENT||||4(100)||

|1|SORTAGGREGATE||1|10|||

|2|TABLEACCESSBYINDEXROWID|T|1|10|4(0)|00:00:01|

|*3|INDEXRANGESCAN|I|1||3(0)|00:00:01|

-------------------------------------------------------------------------------------


PredicateInformation(identifiedbyoperationid):

---------------------------------------------------


3-access("ID">:B1)


SQL_IDgp03v5aw085v3,childnumber1

-------------------------------------

SELECTCOUNT(OBJECT_ID)FROMTWHEREID>:B1


Planhashvalue:2966233522


---------------------------------------------------------------------------

|Id|Operation|Name|Rows|Bytes|Cost(%CPU)|Time|

---------------------------------------------------------------------------

|0|SELECTSTATEMENT||||14373(100)||

|1|SORTAGGREGATE||1|10|||

|*2|TABLEACCESSFULL|T|4999K|47M|14373(2)|00:02:53|

---------------------------------------------------------------------------


PredicateInformation(identifiedbyoperationid):

---------------------------------------------------


2-filter("ID">:B1)


可以看到ACS已经工作了，在v$sql_cs_histogram里也为新游标产生了新的行。

SQL>SELECThash_value,sql_id,child_number,bucket_id,COUNT

2FROMv$sql_cs_histogram

3WHEREsql_id='gp03v5aw085v3'

4ORDERBYsql_id,child_number;


HASH_VALUESQL_IDCHILD_NUMBERBUCKET_IDCOUNT

---------------------------------------------------------

3087275875gp03v5aw085v3010

3087275875gp03v5aw085v3001

3087275875gp03v5aw085v3021

3087275875gp03v5aw085v3110

3087275875gp03v5aw085v3100

3087275875gp03v5aw085v3128

到此，相信大家对“ACS与PL/SQL的工作情况分析”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！