大家好，又见面了，我是全栈君。
–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
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