Oracle - SPM固定执行计划

简介:

当一条sql有多个执行计划时,如何通过spm去绑定其中一条执行计划。

Oracle - SPM固定执行计划(一) https://www.cnblogs.com/ddzj01/p/11365541.html

一、前言

生产中偶尔会碰到一些sql,有多种执行计划,其中部分情况是统计信息过旧造成的,重新收集下统计信息就行了。但是有些时候重新收集统计信息也解决不了问题,而开发又在嗷嗷叫,没时间让你去慢慢分析原因的时候,这时临时的解决办法是通过spm去固定一个正确的执行计划,等找到真正原因后再解除该spm。

二、解决办法

1. 通过dbms_xplan.display_cursor查看指定sql都有哪些执行计划

SQL> select * from table(dbms_xplan.display_cursor('&sql_id',null,'TYPICAL PEEKED_BINDS')); 


Enter value for sql_id: 66a4184u0t6hn
old   1: select * from table(dbms_xplan.display_cursor('&sql_id',null,'TYPICAL PEEKED_BINDS'))
new   1: select * from table(dbms_xplan.display_cursor('66a4184u0t6hn',null,'TYPICAL PEEKED_BINDS'))


SQL_ID  66a4184u0t6hn, child number 0
-------------------------------------
select /*for_test*/ * from test1 where object_id = 1

Plan hash value: 4122059633

---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |       |       |   693 (100)|          |
|*  1 |  TABLE ACCESS FULL| TEST1 |   173K|    15M|   693   (1)| 00:00:09 |
---------------------------------------------------------------------------


SQL_ID  66a4184u0t6hn, child number 1
-------------------------------------
select /*for_test*/ * from test1 where object_id = 1

Plan hash value: 2214001748

-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |       |       |     2 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST1     |    11 |  1056 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_TEST1 |       |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

2. 查询该sql的历史执行情况

col snap_id for 99999999                                                                                   
col date_time for a30                                                                                      
col plan_hash for 9999999999                                                                               
col executions for 99999999                                                                                
col avg_etime_s heading 'etime/exec' for 9999999.99                                                        
col avg_lio heading 'buffer/exec' for 99999999999                                                          
col avg_pio heading 'diskread/exec' for 99999999999                                                        
col avg_cputime_s heading 'cputim/exec' for 9999999.99                                                     
col avg_row heading 'rows/exec' for 9999999                                                                
select * from(                                                                                             
select distinct                                                                                            
s.snap_id,                                                                                                 
to_char(s.begin_interval_time,'mm/dd/yy_hh24mi') || to_char(s.end_interval_time,'_hh24mi') date_time,      
sql.plan_hash_value plan_hash,                                                                             
sql.executions_delta executions,                                                                           
(sql.elapsed_time_delta/1000000)/decode(sql.executions_delta,null,1,0,1,sql.executions_delta) avg_etime_s, 
sql.buffer_gets_delta/decode(sql.executions_delta,null,1,0,1,sql.executions_delta) avg_lio,                
sql.disk_reads_delta/decode(sql.executions_delta,null,1,0,1,sql.executions_delta) avg_pio,                 
(sql.cpu_time_delta/1000000)/decode(sql.executions_delta,null,1,0,1,sql.executions_delta) avg_cputime_s,   
sql.rows_processed_total/decode(sql.executions_delta,null,1,0,1,sql.executions_delta) avg_row              
from dba_hist_sqlstat sql, dba_hist_snapshot s                                                             
where sql.instance_number =(select instance_number from v$instance)                                        
and sql.dbid =(select dbid from v$database)                                                                
and s.snap_id = sql.snap_id                                                                                
and sql_id = trim('&sql_id') order by s.snap_id desc)                                                      
where rownum <= 100;                                                                                       

Enter value for sql_id: 66a4184u0t6hn
old  16: and sql_id = trim('&sql_id') order by s.snap_id desc)
new  16: and sql_id = trim('66a4184u0t6hn') order by s.snap_id desc)

  SNAP_ID DATE_TIME                        PLAN_HASH EXECUTIONS  etime/exec  buffer/exec diskread/exec cputim/exec rows/exec
--------- ------------------------------ ----------- ---------- ----------- ------------ ------------- ----------- ---------
       39 08/16/19_1500_1600              2214001748          1         .12        25839          2901         .10    173927
       39 08/16/19_1500_1600              4122059633          3         .11        13992           847         .11    173927

3. 绑定执行计划

从前两步中可以看到该sql有两条执行计划,假如plan_hash_value为’2214001748’才是对的,而此时数据库选择的是另一条执行计划,我们可以通过执行以下function去将执行计划固定为我们想要的。

 var temp number;
begin
:temp := dbms_spm.load_plans_from_cursor_cache(sql_id=>'66a4184u0t6hn', plan_hash_value=>2214001748);
end;
/

例子:

1. 准备测试表

实验环境,使用scott账号,并给scott赋予dba权限

SQL> create table test1 as select * from dba_objects;
SQL> insert into test1 select * from test1;
SQL> update test1 set object_id = 1 where rownum < (select count(*) from test1) - 10;
SQL> commit;

SQL> select object_id, count(*) from test1 group by object_id;


 OBJECT_ID   COUNT(*)
---------- ----------
         1     173927
     82112          1
     82121          1
     82118          1
     82119          1
     82122          1
     82113          1
     82114          1
     82120          1
     82115          1
     82116          1
     82117          1

2. 创建索引并收集统计信息

SQL> create index idx_test1 on test1(object_id) online;

SQL> begin
dbms_stats.gather_table_stats(ownname => 'SCOTT',
tabname => 'TEST1',
cascade => true, 
method_opt => 'for columns object_id size 10',
no_invalidate => false);
end;
/

3. 通过修改优化器模式,模拟同样的sql产生两条不同的执行计划

开启一个窗口A
SQL> set autot trace
SQL> alter session set optimizer_mode = all_rows;  // 11g默认的值
SQL> select /*for_test*/ * from test1 where object_id = 1;


Execution Plan
----------------------------------------------------------
Plan hash value: 4122059633

---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |   173K|    15M|   693   (1)| 00:00:09 |
|*  1 |  TABLE ACCESS FULL| TEST1 |   173K|    15M|   693   (1)| 00:00:09 |
---------------------------------------------------------------------------

 

开启另一个窗口B
SQL> set autot trace
SQL> alter session set optimizer_mode = first_rows_10;
SQL> select /*for_test*/ * from test1 where object_id = 1;


Execution Plan
----------------------------------------------------------
Plan hash value: 2214001748

-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |    11 |  1056 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST1     |    11 |  1056 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_TEST1 |       |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

 

再开启一个窗口C
SQL> select sql_id, sql_text, optimizer_mode, plan_hash_value, child_number from v$sql where sql_text like 'select /*for_test*/ * from test1%';

SQL_ID        SQL_TEXT                                                OPTIMIZER_ PLAN_HASH_VALUE CHILD_NUMBER
------------- ------------------------------------------------------- ---------- --------------- ------------
66a4184u0t6hn select /*for_test*/ * from test1 where object_id = 1    ALL_ROWS        4122059633            0
66a4184u0t6hn select /*for_test*/ * from test1 where object_id = 1    FIRST_ROWS      2214001748            1
 

可以看到,因为优化器模式的不同,相同的sql产生了两条截然不同的执行计划
当optimizer_mode = all_rows为全表扫描,当optimizer_mode = first_rows_10为索引扫描

4. 绑定执行计划

再新开一个窗口D,执行
SQL> set autot trace
SQL> select /*for_test*/ * from test1 where object_id = 1;


Execution Plan
----------------------------------------------------------
Plan hash value: 4122059633

---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |   173K|    15M|   693   (1)| 00:00:09 |
|*  1 |  TABLE ACCESS FULL| TEST1 |   173K|    15M|   693   (1)| 00:00:09 |
---------------------------------------------------------------------------


可以看到执行计划为全表扫描,跟窗口A一样,这个是正常的

通过执行以下function去将执行计划固定为索引扫描
SQL> var temp number;
SQL> begin
:temp := dbms_spm.load_plans_from_cursor_cache(sql_id=>'66a4184u0t6hn', plan_hash_value=>2214001748);
end;
/

再执行以下sql
SQL> select /*for_test*/ * from test1 where object_id = 1;


Execution Plan
----------------------------------------------------------
Plan hash value: 2214001748

-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |    11 |  1056 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST1     |    11 |  1056 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_TEST1 |   173K|       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

Note
-----
   - SQL plan baseline "SQL_PLAN_9657urkb9u2tnf24a05ff" used for this statement

可以看到spm已经生效了

删除spm

当我们找到sql执行计划突变的原因了,解决问题之后,就可以删除spm了。如何删除spm呢?

  • 新开窗口E,查看当前sql的执行计划基线
SQL> select sql_handle, plan_name, origin from dba_sql_plan_baselines where sql_text like 'select /*for_test*/ * from test1%';

SQL_HANDLE                     PLAN_NAME                      ORIGIN
------------------------------ ------------------------------ --------------
SQL_9314fabc969d0b34           SQL_PLAN_9657urkb9u2tnf24a05ff MANUAL-LOAD
SQL_9314fabc969d0b34           SQL_PLAN_9657urkb9u2tnfe026eff AUTO-CAPTURE
 

可以看到该sql有两条PLAN_NAME,一个是系统自动捕获的,一个是我们手工绑定的,反正我们不再需要这个了,统统删除

  • 通过执行以下function去将执行计划基线删除
 var temp number;
 begin
:temp := dbms_spm.drop_sql_plan_baseline(sql_handle=>'SQL_9314fabc969d0b34', plan_name=>NULL);
end;
/
  • 查看当前sql的执行计划基线
SQL> select sql_handle, plan_name, origin from dba_sql_plan_baselines where sql_text like 'select /*for_test*/ * from test1%';
no rows selected
  • 再在窗口D中执行以下sql
SQL> select /*for_test*/ * from test1 where object_id = 1;


Execution Plan
----------------------------------------------------------
Plan hash value: 4122059633

---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |   173K|    15M|   693   (1)| 00:00:09 |
|*  1 |  TABLE ACCESS FULL| TEST1 |   173K|    15M|   693   (1)| 00:00:09 |
---------------------------------------------------------------------------

可以看到执行计划又变成默认的全表扫描了

如何给一条sql注入一个新的执行计划,去替换原始的执行计划。

Oracle - SPM固定执行计划(二) https://www.cnblogs.com/ddzj01/p/11377049.html

二、解决办法

1. 生成初始执行计划所对应的sql plan baseline

begin
:temp := dbms_spm.load_plans_from_cursor_cache(
sql_id => '原目标sql的sql_id',
plan_hash_value => 原目标sql的plan hash value);
end;
/
  1. 查出该sql的sql_handle
select sql_handle, sql_text, plan_name, origin from dba_sql_plan_baselines where sql_text like '原目标sql的sql_text%';
  1. 生成新的sql plan baseline
begin
:temp := dbms_spm.load_plans_from_cursor_cache(
sql_id => '加入合适hint后改写的sql的sql_id',
plan_hash_value => 加入合适hint后改写的sql的plan hash value,
sql_handle => '原目标sql在步骤(1)中所产生的sql_handle');
end;
/
  1. 删除步骤(1)中所产生的sql plan baseline
begin
:temp := dbms_spm.drop_sql_plan_baseline(
sql_handle => '原目标sql在步骤(1)中的sql_handle',
plan_name => '原目标sql在步骤(1)中的plan_name');
end;
/

例子:

实验环境,使用scott账号,并给scott赋予dba权限(实际上scott只需要administer sql management object权限就可以使用spm)

创建表和索引,并收集统计信息

SQL> create table test2 as select * from dba_objects;
SQL> create index idx_test2 on test2(object_id) online;

SQL> begin
dbms_stats.gather_table_stats(ownname=>'SCOTT',
tabname=>'TEST2',
cascade=>true,
no_invalidate=>false);
end;
/

执行原始的sql

SQL> set autot trace
SQL> select * from test2 where object_id=20;


Execution Plan
----------------------------------------------------------
Plan hash value: 4047680367

-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |     1 |    98 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST2     |     1 |    98 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_TEST2 |     1 |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

可以看到原始sql的执行计划为索引范围扫描

新开一个窗口,查原始sql的sql_id和plan_hash_value

SQL> col sql_id for a20
SQL> col sql_text for a40
SQL> select sql_id, plan_hash_value, sql_text from v$sqlarea where sql_text like 'select * from test2 where object_id=20%';

SQL_ID               PLAN_HASH_VALUE SQL_TEXT
-------------------- --------------- ----------------------------------------
4tm6j886yvzj3             4047680367 select * from test2 where object_id=20
 

将原始sql语句加入基线

SQL> var temp number;
SQL> begin 
:temp := dbms_spm.load_plans_from_cursor_cache(sql_id=>'4tm6j886yvzj3', plan_hash_value=>4047680367);
end;
/

查看原始sql的基线

SQL> col sql_handle for a24
SQL> col sql_text for a40
SQL> col plan_name for a35
SQL> select sql_handle, sql_text, plan_name, origin from dba_sql_plan_baselines where sql_text like 'select * from test2 where object_id=20%';

SQL_HANDLE               SQL_TEXT                                 PLAN_NAME                           ORIGIN
------------------------ ---------------------------------------- ----------------------------------- --------------
SQL_20df29fdb3e8ac52     select * from test2 where object_id=20   SQL_PLAN_21rt9zqtyjb2k60b1ef84      MANUAL-LOAD
 

对原始sql加hint,执行新的sql

SQL> select /*+ full(test2) */ * from test2 where object_id=20;

获得新sql语句的sql_id和plan_hash_value

SQL> select sql_id, plan_hash_value, sql_text from v$sqlarea where sql_text like 'select /*+ full(test2) */%';

SQL_ID               PLAN_HASH_VALUE SQL_TEXT
-------------------- --------------- ----------------------------------------
11cptg7m2vcwr              300966803 select /*+ full(test2) */ * from test2 w
                                     here object_id=20
 

将新的sql_id和plan_hash_value加入到原始sql的基线中

SQL> var temp number;
SQL> begin
:temp := dbms_spm.load_plans_from_cursor_cache(sql_id=>'11cptg7m2vcwr', plan_hash_value=>300966803, sql_handle =>'SQL_20df29fdb3e8ac52');
end;
/

查看原始sql的基线

SQL> select sql_handle, sql_text, plan_name, origin from dba_sql_plan_baselines where sql_text like 'select * from test2 where object_id=20%';

SQL_HANDLE               SQL_TEXT                                 PLAN_NAME                           ORIGIN
------------------------ ---------------------------------------- ----------------------------------- --------------
SQL_20df29fdb3e8ac52     select * from test2 where object_id=20   SQL_PLAN_21rt9zqtyjb2k60b1ef84      MANUAL-LOAD
SQL_20df29fdb3e8ac52     select * from test2 where object_id=20   SQL_PLAN_21rt9zqtyjb2k99963deb      MANUAL-LOAD

可以看到新的执行计划plan_name为SQL_PLAN_21rt9zqtyjb2k99963deb已经加到原始sql的基线中了

删除旧的sql_plan

SQL> var temp number;
SQL> begin
:temp := dbms_spm.drop_sql_plan_baseline(sql_handle =>'SQL_20df29fdb3e8ac52', plan_name=>'SQL_PLAN_21rt9zqtyjb2k60b1ef84');
end;
/

新开一个窗口,再运行原始sql语句

SQL> set autot trace
SQL> select * from test2 where object_id=20;


Execution Plan
----------------------------------------------------------
Plan hash value: 300966803

---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |     1 |    98 |   347   (1)| 00:00:05 |
|*  1 |  TABLE ACCESS FULL| TEST2 |     1 |    98 |   347   (1)| 00:00:05 |
---------------------------------------------------------------------------

Note
-----
   - SQL plan baseline "SQL_PLAN_21rt9zqtyjb2k99963deb" used for this statement

可以看到原始sql的执行计划已经改变了。

四、总结

spm只是一个临时应急解决方案,数据库出现执行计划不正确,应该从源头查找原因,比如说统计信息,索引是否失效等等。

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