Oracle AWR 阙值影响历史执行计划

--环境，下面的演示基于Oracle 10g
scott@CNMMBO> select * from v$version where rownum<2;

BANNER
----------------------------------------------------------------
Oracle Database 10g Release 10.2.0.3.0 - 64bit Production

--下面的查询awr配置
scott@CNMMBO> select * from dba_hist_wr_control;

      DBID SNAP_INTERVAL        RETENTION                 TOPNSQL
---------- -------------------- ------------------------- ----------
 938506715 +00000 01:00:00.0    +00007 00:00:00.0         DEFAULT

--发布sql查询
scott@CNMMBO> select * from dept where loc='CHICAGO';

    DEPTNO DNAME          LOC
---------- -------------- -------------
        30 SALES          CHICAGO

--获得sql_id
scott@CNMMBO> @my_last_sql

ADDRESS          HASH_VALUE SQL_ID        COMMAND_TYPE      PIECE SQL_TEXT
---------------- ---------- ------------- ------------ ---------- ------------------------------------------
000000009F942760 2626775672 2jbkb5qf92ums            3          0 select * from dept where loc='CHICAGO'

--从v$sql_plan获得缓冲区的执行计划
scott@CNMMBO> get sql_plan_curr.sql
  1  set linesize 135
  2  col id format 99
  3  col operation format a25
  4  col options format a25
  5  col object_name format a25 wrap
  6  SELECT id,
  7           operation,
  8           options,
  9           object_name,
 10           bytes,
 11           cpu_cost,
 12           io_cost
 13  FROM v$sql_plan
 14     WHERE sql_id = '&input_sql_id'
 15* ORDER BY id;
scott@CNMMBO> @sql_plan_curr.sql      -->此时可以查询到对应sql的执行计划
Enter value for input_sql_id: 2jbkb5qf92ums

 ID OPERATION                 OPTIONS                   OBJECT_NAME      BYTES   CPU_COST    IO_COST
--- ------------------------- ------------------------- --------------- ------- ---------- ----------
  0 SELECT STATEMENT
  1 TABLE ACCESS              FULL                      DEPT                20      36567          3

--下面尝试从dba_hist_sql_plan获得执行计划
scott@CNMMBO> get sql_plan_his.sql
  1  set linesize 135
  2  col id format 99
  3  col operation format a25
  4  col object_name format a25 wrap
  5  SELECT id,
  6           operation,
  7           options,
  8           object_name,
  9           bytes,
 10           cpu_cost,
 11           io_cost
 12      FROM dba_hist_sql_plan
 13     WHERE sql_id = '&input_sql_id'
 14* ORDER BY id;
scott@CNMMBO> @sql_plan_his     --查询无法获得执行计划
Enter value for input_sql_id: 2jbkb5qf92ums

no rows selected

scott@CNMMBO> exec dbms_workload_repository.create_snapshot();  -->执行一次快照，写入缓冲区的内容倒snapsho

PL/SQL procedure successfully completed.

scott@CNMMBO> @sql_plan_his     -->依旧无法获得执行计划
Enter value for input_sql_id: 2jbkb5qf92ums

no rows selected

--下面我们将topnsql参数设置为最大值，以确保任意sql只要执行一次即可写入到快照
scott@CNMMBO> exec dbms_workload_repository.modify_snapshot_settings(topnsql=>'MAXIMUM');

PL/SQL procedure successfully completed.

--校验awr配置
scott@CNMMBO> select * from dba_hist_wr_control;

      DBID SNAP_INTERVAL        RETENTION                 TOPNSQL
---------- -------------------- ------------------------- ----------
 938506715 +00000 01:00:00.0    +00007 00:00:00.0         MAXIMUM

--先看看dba_hist_sql_plan，此时肯定是不存在，因为没有执行快照
scott@CNMMBO> @sql_plan_his
Enter value for input_sql_id: 2jbkb5qf92ums

no rows selected

--再次执行一下原来的sql语句
scott@CNMMBO> select * from dept where loc='CHICAGO';

    DEPTNO DNAME          LOC
---------- -------------- -------------
        30 SALES          CHICAGO

--此时执行手动创建快照实现写入
scott@CNMMBO> exec dbms_workload_repository.create_snapshot();

PL/SQL procedure successfully completed.

--再次查看，sql执行计划已经写入到awr快照
scott@CNMMBO> @sql_plan_his
Enter value for input_sql_id: 2jbkb5qf92ums

 ID OPERATION                 OPTIONS                   OBJECT_NAME      BYTES   CPU_COST    IO_COST
--- ------------------------- ------------------------- --------------- ------- ---------- ----------
  0 SELECT STATEMENT
  1 TABLE ACCESS              FULL                      DEPT                20      36567          3

--同时我们也可以通过DBMS_XPLAN.display_awr查看到相应的执行计划
--Author : Robinson
-- Blog  : http://blog.csdn.net/robinson_0612
scott@CNMMBO> @sql_plan_disp_awr
Enter value for input_sqlid: 2jbkb5qf92ums

PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------
SQL_ID 2jbkb5qf92ums
--------------------
select * from dept where loc='CHICAGO'

Plan hash value: 3383998547

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |     3 (100)|          |
|   1 |  TABLE ACCESS FULL| DEPT |     1 |    20 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------

13 rows selected.

--恢复缺省值
scott@CNMMBO> exec dbms_workload_repository.modify_snapshot_settings(topnsql=>'DEFAULT');

PL/SQL procedure successfully completed.