--因为生产环境运行的sql变化较快，版本号公布比較频繁，造成sql的运行计划不是非常稳定。常常会有一些性能非常查的sql出现

--对于这些sql，我们能够使用sql_plan_baseline对运行计划进行绑定，从而使运行计划固定下来

--前提是sql最好使用绑定变量。就算有的没有绑定变量，确定字段的值不会改变才行。由于是针对sql_id进行的绑定，假设sql文本改变，绑定也就无意义了

详细步骤：

--1、找到问题sql，假设查询sql的运行计划，假设有合适的运行计划。直接进行绑定

--查询sql运行计划相应的PLAN_HASH_VALUE

SELECT DISTINCT(PLAN_HASH_VALUE) FROM V$SQL_PLAN t WHERE SQL_ID = '010cv4dvf6swv' and child_number='0'

--绑定好的运行计划：

declare

  l_pls number;

begin

  l_pls := DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE(sql_id  => '524wzct86gu1d',

                                                 plan_hash_value => 2554538542,

                                                 enabled         => 'YES');

end;

/

2、假设没有合适的运行计划，就要通过自己分析，运用一些hint让sql产生比較好的运行计划

--须要绑定的sql

--oldSQL(id PLAN_HASH_VALUE)

524wzct86gu1d

2554538542

--新的sql

--newSQL(id PLAN_HASH_VALUE)

010cv4dvf6swv

756701203

--查询新的运行计划的sql_id

select * from v$sql where sql_text like '%zhruoyu%' --通过在hint中加一下特殊字符来查找

---新建制定SQLID的BASELINE依据old_sql id,PLAN_HASH_VALUE

declare

  l_pls number;

begin

  l_pls := DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE(sql_id    => '524wzct86gu1d',

                                                 plan_hash_value => 2554538542,

                                                 enabled         => 'NO');  --注意这里是no

end;

/

---确定原始运行计划的 sql_handle

select sql_handle, plan_name, origin, enabled, accepted,fixed,creator,optimizer_cost,sql_text

from dba_sql_plan_baselines where origin = 'MANUAL-LOAD' order by created desc

 

SQL_HANDLE:SQL_66108ad9595208fc                                     

PLAN_NAME:SQL_PLAN_6c44av5cp427w65e519aa

---与正确的运行计划做关联

declare

  l_pls number;

begin

  l_pls := DBMS_SPM.load_plans_from_cursor_cache(sql_id          => '010cv4dvf6swv', -- new_SQL_ID'

                                                 plan_hash_value => 756701203, --new_plan_hash_value

                                                 sql_handle      => 'SQL_66108ad9595208fc' --OLD_handle

                                                 );

end;

/

---删除错误的运行计划

declare

  l_pls number;

begin

  l_pls := DBMS_SPM.DROP_SQL_PLAN_BASELINE(sql_handle => 'SQL_66108ad9595208fc', --sql_handle_for_original

                                           plan_name  => 'SQL_PLAN_6c44av5cp427w65e519aa' --sql_plan_name_for_original                                       

                                           );

end;

/

--检查一下

select sql_handle, plan_name, origin, enabled, accepted,fixed,creator,optimizer_cost,sql_text

from dba_sql_plan_baselines where origin = 'MANUAL-LOAD' and sql_handle='SQL_66108ad9595208fc'

--完毕