執行計劃變化的處理

oracle 10g

4、操做步驟

方法一：

    先嚐試用 oracle自帶的調優包獲得建議，若是建議裏能夠採用profile獲得原來的執行計劃，則接受建議，執行相關命令；若是建議裏沒有原來的執行計劃，轉到方法二。

注意：將下面 SQL中的「8sjqpgjwztzm8」替換爲問題SQL的sql_id便可運行。

步驟1、建立任務

set serverout on

DECLARE

 l_sql_tune_task_id VARCHAR2(100);

BEGIN

 l_sql_tune_task_id := DBMS_SQLTUNE.create_tuning_task(sql_id       => '8sjqpgjwztzm8',

                                                        scope       => DBMS_SQLTUNE.scope_comprehensive,

                                                        time_limit => 600,

                                                        task_name   => '8sjqpgjwztzm8_tuning_task',

                                                        description => 'Tuning task for statement 8sjqpgjwztzm8.');

 DBMS_OUTPUT.put_line('l_sql_tune_task_id: ' || l_sql_tune_task_id);

END;

步驟2、確認任務已經建立

--有返回結果表示正常

select task_name

 from dba_advisor_log

 where owner = 'SYS'

   and task_name = '8sjqpgjwztzm8_tuning_task';

運行任務

Execute dbms_sqltune.Execute_tuning_task (task_name => '8sjqpgjwztzm8_tuning_task');

步驟3、確認任務狀態

select status

 from dba_advisor_log

 where task_name = '8sjqpgjwztzm8_tuning_task';

步驟4、打印報表

--查看調優建議，這一步能夠獲得調優建議，若是有須要的執行計劃，則接受 profile

set long 999999

set longchunksize 1000

set lin 140 pages 1000

select dbms_sqltune.report_tuning_task('8sjqpgjwztzm8_tuning_task')

 from dual;

 

這裏舉個例子，若是確認執行計劃可用，運行紅框命令便可。

步驟5、刪除任務

--調優完成後此任務再也不須要

exec dbms_sqltune.DROP_TUNING_TASK(task_name => '8sjqpgjwztzm8_tuning_task');

 

方法二：

因統計信息變化致使執行計劃效率變差的狀況，出現的頻率仍是很高的，但願輪班的同事，至少是值班班長有能力去處理這類的問題。

 

基本的思路以下，你們須要不斷在實戰中鍛鍊本身，作幾回就熟了，不要怯戰。

步驟1、查看歷史信息

--經過看 awr的歷史信息，很容易就知道執行計劃的效率更高

select s.instance_number,

       to_char(sn.end_interval_time, 'YYYYMMDD HH24:MI:SS'),

       s.plan_hash_value,

       s.executions_delta,

       round(s.elapsed_time_delta / s.executions_delta),

       round(s.BUFFER_GETS_delta / s.executions_delta),

       round(s.CPU_TIME_delta / s.executions_delta)

 from dba_hist_snapshot sn, sys.WRH$_SQLSTAT s

 where s.snap_id = sn.snap_id

   and s.sql_id = '1gu8t96d0bdmu'

   and s.instance_number = sn.instance_number

   and s.executions_delta > 0

 order by sn.end_interval_time desc

步驟2、對比新舊執行計劃區別

--對比效率高和低的執行計劃的區別

SELECT * FROM table(DBMS_XPLAN.DISPLAY_AWR('&sql_id',null,null,'ALL'));

 

步驟3、作hint 獲得好的執行計劃

通常狀況下，經過 index， leading，use_hash or use_nl  就能搞定，估計80%~90%的sql用這幾個hint就能搞定了

實在搞不定的，再去找主管 dba看下

對於 10g以上庫，有個理論上方法，將DG 設置迴歸點後激活，將sql相關的對象的統計信息回退到 好執行計劃的時間點

對 explain plan for sqlstat 作10053 的trace，好的執行計劃的hint就能直接在trace文件中找到

反正無論怎麼說，只要肯花點時間，總能作出來

 

步驟4、outline 互換

第一步：先爲加Hint後的好的執行計劃生成outline：

CREATE OR REPLACE OUTLINE zhuofhb for category special ON

SELECT T1.DISPATCHNO,

       T1.AUTO_TASK_NO,

       T1.TASK_NO,

       T1.REPORT_ID,

       T1.TASK_DEPT,

       T1.HANDLER_ID,

       T1.CAR_MARK,

       T1.ARRIVE_TIME,

       T1.ARRIVE_TIMES,

       T1.TASK_STATUS,

       T1.APPLY_USER,

       T1.APPLY_TACHE_ID,

       T1.TASK_ATTRIBUTE,

       T1.REMARK,

       T1.CREATED_BY,

       T1.CREATED_DATE,

       T1.UPDATE_BY,

       T1.UPDATE_DATE,

       T1.LOCAL_FLAG

 FROM T_AUTO_DISPATCH_TASK T1

 WHERE (T1.TASK_STATUS = '2' OR T1.AUTO_TASK_NO IS NULL)

   AND EXISTS (SELECT *

          FROM (SELECT DISTINCT T.DISPATCHNO

                  FROM (SELECT T2.DISPATCHNO

                          FROM T_AUTO_DISPATCH_COMMON T2

                         WHERE T2.SYNCSTATUS = '0'

                           AND T2.REPORTFLAG = 'Y'

                           AND T2.CASE_STATUS = '1'

                           AND EXISTS

                         (SELECT 1

                                  FROM C_ACC_SYNC_INFO T

                                 WHERE T.SYNC_STATUS
||= '2'

                                   AND T.CASENO = T2.CASENO)

                         ORDER BY T2.CASE_DIS_TIME) T

                 WHERE ROWNUM < 20) XX

         WHERE XX.DISPATCHNO = T1.DISPATCHNO)

 ORDER BY T1.ARRIVE_TIME

;   

第二步：再爲舊的壞的執行計劃生成outline：

CREATE OR REPLACE OUTLINE zhuofha for category special ON

SELECT T1.DISPATCHNO,

       T1.AUTO_TASK_NO,

       T1.TASK_NO,

       T1.REPORT_ID,

       T1.TASK_DEPT,

       T1.HANDLER_ID,

       T1.CAR_MARK,

       T1.ARRIVE_TIME,

       T1.ARRIVE_TIMES,

       T1.TASK_STATUS,

       T1.APPLY_USER,

       T1.APPLY_TACHE_ID,

       T1.TASK_ATTRIBUTE,

       T1.REMARK,

       T1.CREATED_BY,

       T1.CREATED_DATE,

       T1.UPDATE_BY,

       T1.UPDATE_DATE,

       T1.LOCAL_FLAG

 FROM T_AUTO_DISPATCH_TASK T1

 WHERE (T1.TASK_STATUS = '2' OR T1.AUTO_TASK_NO IS NULL)

   AND EXISTS (SELECT *

          FROM (SELECT DISTINCT T.DISPATCHNO

                  FROM (SELECT T2.DISPATCHNO

                          FROM T_AUTO_DISPATCH_COMMON T2

                         WHERE T2.SYNCSTATUS = '0'

                           AND T2.REPORTFLAG = 'Y'

                           AND T2.CASE_STATUS = '1'

                           AND EXISTS

                         (SELECT 1

                                  FROM C_ACC_SYNC_INFO T

                                 WHERE T.SYNC_STATUS = '2'

                                   AND T.CASENO = T2.CASENO)

                         ORDER BY T2.CASE_DIS_TIME) T

                 WHERE ROWNUM < 20) XX

         WHERE XX.DISPATCHNO = T1.DISPATCHNO)

 ORDER BY T1.ARRIVE_TIME

;   

第三步：將兩個outline的名字互換，讓outline生效

UPDATE OUTLN.OL$HINTS

SET OL_NAME=DECODE(OL_NAME,'ZHUOFHB','ZHUOFHA','ZHUOFHA','ZHUOFHB')

WHERE OL_NAME IN ('ZHUOFHB','ZHUOFHA');

 

exec dbms_outln.update_signatures;

alter system set use_stored_outlines=special;

第四步：刪除不用的outline

--這個必定要作，不然之後他們下發優化後的 sql語句後，會用到這個outline中的壞的執行計劃

drop outline zhuofhb;

第五步：驗證

驗證執行計劃，對 pol_main不走全表掃描就對了  

select hash_value,sql_text,outline_category,child_number from v$sql where hash_value=3671808433