ITPub博客

首页 > 数据库 > Oracle > 使用优化器性能视图获取SQL语句执行环境

使用优化器性能视图获取SQL语句执行环境

Oracle 作者:最阴暗的阳光 时间:2013-12-30 13:12:38 0 删除 编辑
 Oracle SQL语句的运行环境分为多个不同的层次,主要包括实例级别,会话级别,语句级别,其优先级依次递增。即语句级别的执行环境具
有最高的优先权,会话级别次之,实例级别最低。反过来,实例级别的环境设置影响全局,而会话级别的则影响当前会话,语句级别的设置当然
也就只影响当前语句。由此可知,运行环境中每一个环节的参数都对最终的数据库性能或所执行的SQL语句有直接的影响。因此在对数据库优化
或调试SQL时,获得当前SQL语句运行环境显得尤为重要。为此,Oracle提供了三个重要的视图来获取不同级别的参数信息。
一、优化器性能视图名字

--下面的三个性能视图分别对应到不同的级别
scott@ORCL> select table_name from dict where table_name like 'V$%OPTIMIZER_ENV';
TABLE_NAME
------------------------------
V$SYS_OPTIMIZER_ENV
V$SES_OPTIMIZER_ENV
V$SQL_OPTIMIZER_ENV
--注:上述的3个视图实际上是Oracle 10053事件中参数的一个子集
二、实例级别执行环境(视图V$SYS_OPTIMIZER_ENV)

--提供实例级别的环境执行的信息。Oracle 优化器在为SQL语句生成执行计划时,会 据实例级别参数的值来确定,如 optimizer_mode 用于
--确定优化器的模式,optimizer_index_cost_adj用于确定全表扫描与索引扫描之间成本开销的比值等。
--实例级别的参数可以使用下面的方式来设置
alter system set parameter=value scope=memory | both |spfile;
--我们来看看当前实例级别的运行环境
scott@ORCL> select
  name,
  value,
  isdefault
  from
  v$sys_optimizer_env
  order by 3,1;
NAME                               |VALUE          |ISD
-----------------------------------|---------------|---
statistics_level                   |all            |NO     -->非缺省值在此显示为NO
active_instance_count              |1              |YES
bitmap_merge_area_size             |1048576        |YES
cpu_count                          |1              |YES
cursor_sharing                     |exact          |YES
hash_area_size                     |131072         |YES
optimizer_dynamic_sampling         |2              |YES
optimizer_features_enable          |10.2.0.1       |YES
optimizer_index_caching            |0              |YES
optimizer_index_cost_adj           |100            |YES
optimizer_mode                     |all_rows       |YES
optimizer_secure_view_merging      |true           |YES
parallel_ddl_mode                  |enabled        |YES
parallel_dml_mode                  |disabled       |YES
parallel_execution_enabled         |true           |YES
parallel_query_mode                |enabled        |YES
parallel_threads_per_cpu           |2              |YES
pga_aggregate_target               |59392 KB       |YES
query_rewrite_enabled              |true           |YES
query_rewrite_integrity            |enforced       |YES
skip_unusable_indexes              |true           |YES
sort_area_retained_size            |0              |YES
sort_area_size                     |65536          |YES
star_transformation_enabled        |false          |YES
workarea_size_policy               |auto           |YES
--从上面的查询结果可知,当前系统中仅有statistics_level参数使用了非缺省值,statistics_level参数的缺省值为typical,而此处为all。
--对于实例级别任意参数的修改其影响都是全局的, 此应当慎重。当然,如果某个参数设置的不合理,其影响也是全局的, 此对于实例级别
--参数的合理设置,可以避免成百上千枯燥的SQL语句调整,反之整个数据库性能急剧下降也可能是 为实例级别参数设置不当所致。
三、会话级别执行环境(视图V$SES_OPTIMIZER_ENV)


--与实例级别相对应的会话级别视图是V$SES_OPTIMIZER_ENV。此时session 级别的参数值会优先于实例级别的参数值。
--我们可以通过V$SYS_OPTIMIZER_ENV与V$SES_OPTIMIZER_ENV来获得当前或某个特定session的所有session级别参数值。
scott@ORCL> show parameter cursor_shar
NAME                                |TYPE       |VALUE
------------------------------------|-----------|------------------
cursor_sharing                      |string     |EXACT
scott@ORCL> alter session set cursor_sharing=force;
Session altered.
scott@ORCL> show parameter cursor_shar
NAME                                |TYPE       |VALUE
------------------------------------|-----------|------------------
cursor_sharing                      |string     |FORCE
scott@ORCL> alter session set optimizer_mode=first_rows_100;
Session altered.
scott@ORCL> show parameter optimizer_mode
NAME                                |TYPE                            |VALUE
------------------------------------|--------------------------------|--------------------
optimizer_mode                      |string                          |FIRST_ROWS_100 
scott@ORCL> alter session set db_file_multiblock_read_count=128;
Session altered.
scott@ORCL> select username,sid,serial# from v$session where username='SCOTT';
USERNAME                           SID|   SERIAL#
------------------------------|----------|----------
SCOTT                              159|         5
scott@ORCL> select name,value,isdefault
  from v$ses_optimizer_env
  where sid=&input_sid
  minus
  select name,value,isdefault
  from v$sys_optimizer_env;
Enter value for input_sid: 159
old   3: where sid=&input_sid
new   3: where sid=159
NAME                               |VALUE          |ISD
-----------------------------------|---------------|---
_db_file_optimizer_read_count      |128            |NO
cursor_sharing                     |force          |NO
optimizer_mode                     |first_rows_100 |NO
四、语句级别执行环境(视图V$SQL_OPTIMIZER_ENV)


--影响SQL语句运行的执行环境受到实例级别以及会话级别之外,最后的,优先级最高的级别即是语句级别。 此语句级别的设置直接影响最终
--SQL语句执行计划的产生。SQL语句级别的参数设置是通过提示来完成的。 
--在下面的例子中,我们通过为同一SQL 语句使用提示来使其运行在不同的环境之中。
scott@ORCL> select ename,job,sal from emp where empno=7369;  -->此SQL语句会 据实例与会话级别的优化器环境
                                                                            -->的设置来生成SQL执行计划并执行
ENAME     |JOB           SAL                                             -->此时的no_hint不是一个有效的提示,被当成注释
----------|---------|----------
Henry     |CLERK        1400
scott@ORCL> select ename,job,sal from emp where empno=7369;  -->此时该SQL语句使用了all_rows提示
                                                                             -->注,此语句与上一语句尽管得到的相同的结果
ENAME     |JOB           SAL                                              -->但运行在不同的优化器环境模式之中
----------|---------|----------                                              -->两者会有不同的sql_id
Henry     |CLERK        1400 
scott@ORCL> show parameter optimizer_index_cost_adj                          -->查看参数设置
NAME                                |TYPE       |VALUE
------------------------------------|-----------|------------------------------
optimizer_index_cost_adj            |integer    |100
scott@ORCL> show parameter cursor_sharing                                    -->查看参数设置
NAME                                |TYPE       |VALUE
------------------------------------|-----------|------------------------------
cursor_sharing                      |string     |EXACT
scott@ORCL> select avg(sal) from emp;                                        -->聚合运算
  AVG(SAL)
----------
      2335
scott@ORCL> alter session set cursor_sharing=force;                          -->基于session级别修改参数
Session altered.
scott@ORCL> alter session set optimizer_index_cost_adj=80;                   -->基于session级别修改参数
Session altered.
scott@ORCL> select avg(sal) from emp;                                        -->再次聚合运算
  AVG(SAL)
----------
      2335
-->下面的查询得到同一SQL语句由于不同运行环境的sql_id,child_number等  
scott@ORCL> select sql_id, child_number, sql_text,optimizer_env_hash_value oehv,child_address
  from v$sql where sql_text like '%avg(sal)%' and sql_text not like '%from v$sql%';
SQL_ID       |CHILD_NUMBER|SQL_TEXT                               OEHV|CHILD_AD
-------------|------------|-----------------------------------|----------|--------
5du23va3p3ad0|           0|select avg(sal) from emp           |2196913643|3015F434
5du23va3p3ad0|           1|select avg(sal) from emp           |3293423667|2CD868A0
-->获得同一SQL语句父游 与子游 执行环境不同的地方
scott@ORCL> select se0.name,se0.value as value_child_0,se1.value as value_child_1
  from v$sql_optimizer_env se0
  inner join v$sql_optimizer_env se1
  on se0.sql_id=se1.sql_id
  where se0.sql_id='&input_sql_id'
  and se0.child_number=0
  and se1.child_number=1
  and se0.name=se1.name
  and se0.value<>se1.value;
Enter value for input_sql_id: 5du23va3p3ad0
old   5: where se0.sql_id='&input_sql_id'
new   5: where se0.sql_id='5du23va3p3ad0'
NAME                                    |VALUE_CHILD_0            |VALUE_CHILD_1
----------------------------------------|-------------------------|-------------------------
cursor_sharing                          |exact                    |force
optimizer_index_cost_adj                |100                      |80
-->获得上一SQL语句运行时优化器的详细信息
-->我们看到父游 与子游 的信息全部被列出来
scott@ORCL> select address, name, value, isdefault,child_number
  from v$sql_optimizer_env
  where sql_id = '5du23va3p3ad0'
  order by child_number, isdefault, name;
ADDRESS |NAME                                    |VALUE                    |ISD|CHILD_NUMBER
--------|----------------------------------------|-------------------------|---|------------
30177094|sqlstat_enabled                         |true                     |NO |           0
30177094|statistics_level                        |all                      |NO |           0
30177094|active_instance_count                   |1                        |YES|           0
30177094|bitmap_merge_area_size                  |1048576                  |YES|           0
30177094|cpu_count                               |1                        |YES|           0
30177094|cursor_sharing                          |exact                    |YES|           0
30177094|hash_area_size                          |131072                   |YES|           0
30177094|optimizer_dynamic_sampling              |2                        |YES|           0
30177094|optimizer_features_enable               |10.2.0.1                 |YES|           0
30177094|optimizer_index_caching                 |0                        |YES|           0
30177094|optimizer_index_cost_adj                |100                      |YES|           0
30177094|optimizer_mode                          |all_rows                 |YES|           0
30177094|optimizer_secure_view_merging           |true                     |YES|           0
30177094|parallel_ddl_mode                       |enabled                  |YES|           0
30177094|parallel_dml_mode                       |disabled                 |YES|           0
30177094|parallel_execution_enabled              |true                     |YES|           0
30177094|parallel_query_mode                     |enabled                  |YES|           0
30177094|parallel_threads_per_cpu                |2                        |YES|           0
30177094|pga_aggregate_target                    |59392 KB                 |YES|           0
30177094|query_rewrite_enabled                   |true                     |YES|           0
30177094|query_rewrite_integrity                 |enforced                 |YES|           0
30177094|skip_unusable_indexes                   |true                     |YES|           0
30177094|sort_area_retained_size                 |0                        |YES|           0
30177094|sort_area_size                          |65536                    |YES|           0
30177094|star_transformation_enabled             |false                    |YES|           0
30177094|workarea_size_policy                    |auto                     |YES|           0
30177094|cursor_sharing                          |force                    |NO |           1
30177094|optimizer_index_cost_adj                |80                       |NO |           1
30177094|sqlstat_enabled                         |true                     |NO |           1
30177094|statistics_level                        |all                      |NO |           1
30177094|active_instance_count                   |1                        |YES|           1
30177094|bitmap_merge_area_size                  |1048576                  |YES|           1
30177094|cpu_count                               |1                        |YES|           1
30177094|hash_area_size                          |131072                   |YES|           1
30177094|optimizer_dynamic_sampling              |2                        |YES|           1
30177094|optimizer_features_enable               |10.2.0.1                 |YES|           1
30177094|optimizer_index_caching                 |0                        |YES|           1
30177094|optimizer_mode                          |all_rows                 |YES|           1
30177094|optimizer_secure_view_merging           |true                     |YES|           1
30177094|parallel_ddl_mode                       |enabled                  |YES|           1
30177094|parallel_dml_mode                       |disabled                 |YES|           1
30177094|parallel_execution_enabled              |true                     |YES|           1
30177094|parallel_query_mode                     |enabled                  |YES|           1
30177094|parallel_threads_per_cpu                |2                        |YES|           1
30177094|pga_aggregate_target                    |59392 KB                 |YES|           1
30177094|query_rewrite_enabled                   |true                     |YES|           1
30177094|query_rewrite_integrity                 |enforced                 |YES|           1
30177094|skip_unusable_indexes                   |true                     |YES|           1
30177094|sort_area_retained_size                 |0                        |YES|           1
30177094|sort_area_size                          |65536                    |YES|           1
30177094|star_transformation_enabled             |false                    |YES|           1
30177094|workarea_size_policy                    |auto                     |YES|           1
52 rows selected.
-->Author : Robinson Cheng 
-->Blog :   http://dong2008hong.blog.163.com
五、总结
1、通过三个重要的优化器性能视图v$sys_optimizer_env,v$ses_optimizer_env,v$sql_optimizer_env可以获得SQL语句的优化器相关的信息
2、三个性能视图获得的数据实际上Oracle 10053 事件的一部分,即也可以通过Oracle 10053 事件进行剖析来得到相同的结果
3、为调试SQL语句设置不同级别的优化器相关参数提供了便利



<!-- 正文结束 -->

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/21443410/viewspace-1115820/,如需转载,请注明出处,否则将追究法律责任。

上一篇: 没有了~
下一篇: 没有了~
请登录后发表评论 登录
全部评论

注册时间:2009-04-21