正文

如何通过outline为SQL语句指定执行计划

IP云
IP云V管理员/3 阅读
11/28
提示：扫一扫查出行
【扫一扫了解最新限行尾号】
复制提示

  • 创建测试表 

以用户jyu连接，创建测试表

SQL> conn jyu/jyu;

Connected.

SQL> create table t (id number, name varchar2(100));

Table created.

SQL> insert into t select rownum,object_name from dba_objects;

47391 rows created.

SQL> commit;

Commit complete.

创建索引

SQL> create index t_idx1 on t(id);

Index created.

收集统计数据

SQL> exec dbms_stats.gather_table_stats('JYU','T');

PL/SQL procedure successfully completed.

  • 执行计划 

查看SQL语句执行计划

SQL> set autotrace traceonly

SQL> select * from t where id=1;

Execution Plan

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

Plan hash value: 3292636276

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

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

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

|   0 | SELECT STATEMENT            |        |     1 |    28 |     2   (0)| 00:00:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| T      |     1 |    28 |     2   (0)| 00:00:01 |

|*  2 |   INDEX RANGE SCAN          | T_IDX1 |     1 |       |     1   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   2 - access("ID"=1)

Note

-----

   - outline "OLD_OUTLN" used for this statement

Statistics

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

          0  recursive calls

          0  db block gets

          4  consistent gets

          0  physical reads

          0  redo size

        576  bytes sent via SQL*Net to client

        492  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          1  rows processed

SQL语句选择了使用索引的执行计划

使用Hint指定语句使用全表扫描的执行计划

SQL> explain plan for select /*+ full(t) */ * from t where id=1;

Explained.

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 2153619298

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

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

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

|   0 | SELECT STATEMENT  |      |     1 |    28 |    50   (2)| 00:00:01 |

|*  1 |  TABLE ACCESS FULL| T    |     1 |    28 |    50   (2)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

PLAN_TABLE_OUTPUT

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

   1 - filter("ID"=1)

13 rows selected.

使用outline固定执行计划 

以sysdba连接数据库

SQL> conn /as sysdba

Connected.

分别为2个SQL语句创建outline

SQL> alter session set current_schema = jyu;

Session altered.

SQL> create or replace outline OLD_OUTLN for category TEMP_PLAN on select * from t where id=1;

Outline created.

SQL> create or replace outline NEW_OUTLN for category TEMP_PLAN on select /*+ full(t) */ * from t where id=1;

Outline created.

交换SQL语句的outline

SQL> create private outline OLFROM from OLD_OUTLN;

Outline created.

SQL> create private outline OLTO from NEW_OUTLN;

Outline created.

SQL> update ol$ set hintcount=(select hintcount from ol$ where ol_name='OLTO') where ol_name='OLFROM';

1 row updated.

SQL> delete from ol$ where ol_name='OLTO';

1 row deleted.

SQL> update ol$ set ol_name='OLTO' where ol_name='OLFROM';

1 row updated.

SQL> commit;

Commit complete.

SQL> execute dbms_outln_edit.refresh_private_outline('OLTO');

PL/SQL procedure successfully completed.

SQL> create or replace outline OLD_OUTLN from private OLTO for category GOOD_PLAN;

Outline created.

SQL> drop outline NEW_OUTLN;

Outline dropped.

  • 设置使用指定的outlines 

有两种方式可在全局设置使用outline

方式一：使用alter system设置(数据库重启后失效)

SQL> conn / as sysdba

Connected.

SQL> alter system set use_stored_outlines=GOOD_PLAN;

System altered.

方式二：通过trigger设置(数据库重启仍然有效)

SQL> create or replace trigger enable_outlines_trig

--Ref : How to Enable USE_STORED_OUTLINES Permanently (Doc ID 560331.1)

after startup on database

begin

  execute immediate('alter system set use_stored_outlines=GOOD_PLAN');

end;

/

  • 检查SQL语句执行计划 

SQL> conn jyu/jyu

Connected.

SQL> set autotrace traceonly

SQL> select * from t where id=1;

Execution Plan

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

Plan hash value: 2153619298

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

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

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

|   0 | SELECT STATEMENT  |      |     1 |    28 |    50   (2)| 00:00:01 |

|*  1 |  TABLE ACCESS FULL| T    |     1 |    28 |    50   (2)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   1 - filter("ID"=1)

Note

-----

   - outline "OLD_OUTLN" used for this statement

Statistics

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

         34  recursive calls

        145  db block gets

        269  consistent gets

          0  physical reads

        576  redo size

        576  bytes sent via SQL*Net to client

        492  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          2  sorts (memory)

          0  sorts (disk)

          1  rows processed

outline生效，SQL语句执行了全表扫描。

  • fix_plan.sh (http://alexzeng.wordpress.com/2013/12/30/how-to-use-hinted-sql-to-fix-bad-sql-plan/) 

#!/bin/bash

if [ $# -lt 3 ]; then

cat <<EOF

Fix given SQL plan using given sql in file

  usage:    fix_plan.sh <hash_value> <hinted_sql_file> <owner>

  examples: fix_plan.sh 716428968 good.sql ALEX

EOF

exit 1

fi

HASH_VALUE=$1

SQL_FILE=$2

OL_OWNER=$3

echo "HASH_VALUE : $HASH_VALUE"

echo "SQL_FILE   : $SQL_FILE"

echo "OL_OWNER   : $OL_OWNER"

echo ""

#Create outline by hash_value

function create_ol_from_hashvalue {

HASH_VALUE=$1

OL_NAME=$2

OL_OWNER=$3

#generate create outline sql

#I didn't use dbms_outln.create_outline, because it cannot create given name outline

# and there's no hash value in V$SQL and DBA_OUTLINES to associate the two

# according to "How To Match a SQL Statement to a Stored Outline (Doc ID 743312.1)"

sqlplus -S "/ as sysdba" > /tmp/tmp_$OL_NAME.sql <<EOF

set feedback off

set serveroutput on size unlimited

declare

v_sqltext varchar2(32000);

begin

  --get sql text

  select dbms_lob.substr(SQL_FULLTEXT, 30000, 1 ) into v_sqltext from v\$sql where hash_value = $HASH_VALUE and rownum=1;

  dbms_output.put_line('alter session set current_schema = $OL_OWNER;');

  v_sqltext := 'create or replace outline $OL_NAME for category TEMP_PLAN on ' || chr(10) || v_sqltext || chr(10) ||';';

  dbms_output.put_line(v_sqltext);

  dbms_output.put_line('exit;');

end;

/

EOF

sqlplus -S "/ as sysdba" @/tmp/tmp_$OL_NAME.sql

}

#Create outline from sql file

function create_ol_from_sqlfile {

SQL_FILE=$1

OL_NAME=$2

OL_OWNER=$3

#generate create outline sql

cat > /tmp/tmp_$OL_NAME.sql <<EOF

alter session set current_schema = $OL_OWNER;

create or replace outline $OL_NAME for category TEMP_PLAN on

`cat $SQL_FILE`

exit;

EOF

sqlplus -S "/ as sysdba" @/tmp/tmp_$OL_NAME.sql

}

#Exchange outlines, make GOOD_SQL plan to GOOD_PLAN category

#Ref: How to Edit a Stored Outline to Use the Plan from Another Stored Outline (Doc ID 730062.1)

function exchange_outline {

OL1=$1

OL2=$2

OL_OWNER=$3

sqlplus -S "/ as sysdba" <<EOF

set feedback off

alter session set current_schema = $OL_OWNER;

create private outline OLFROM from $OL1;

create private outline OLTO from $OL2;

update ol$ set hintcount=(select hintcount from ol$ where ol_name='OLTO') where ol_name='OLFROM';

delete from ol$ where ol_name='OLTO';

update ol$ set ol_name='OLTO' where ol_name='OLFROM';

commit;

execute dbms_outln_edit.refresh_private_outline('OLTO');

create or replace outline $OL1 from private OLTO for category GOOD_PLAN;

drop outline $OL2;

exit;

EOF

}

#display outline

function display_outline {

OL_NAME=$1

OL_OWNER=$2

sqlplus -S "/ as sysdba" <<EOF

set pagesize 1000 linesize 160

set long 32000

col hint format a55

col join_pos format a45

col owner    format a12

col name     format a18

col ts       format a14

col h        format 999

col category format a12

col sql_text format a80

col used     format a6

select name, sql_text, category, used, to_char(TIMESTAMP, 'YY-mm-dd hh24:MI')

 from  dba_outlines

where name = '$OL_NAME' and OWNER = '$OL_OWNER';

select ol_name name, category, hint#, stage# stage, hint_text hint, join_pred join_pos

 from outln.ol\$hints

 where ol_name = '$OL_NAME'

 order by ol_name, hint#;

exit;

EOF

}

#main function

echo "1. Create outline OL_$HASH_VALUE for SQL $HASH_VALUE"

create_ol_from_hashvalue $HASH_VALUE OL_$HASH_VALUE $OL_OWNER

echo "2. Create outline OL_TEMP for SQL in $SQL_FILE"

create_ol_from_sqlfile $SQL_FILE OL_TEMP $OL_OWNER

echo "3. Exchange outline OL_$HASH_VALUE with OL_TEMP, and drop OL_TEMP"

exchange_outline OL_$HASH_VALUE OL_TEMP $OL_OWNER

echo "4. Display final outline for SQL $HASH_VALUE : OL_$HASH_VALUE in category GOOD_PLAN "

display_outline OL_$HASH_VALUE $OL_OWNER

相关阅读

目录[+]