//Oracle默认的隔离级别为Read Committed,因此可能出现不可重复度和幻读;
//MySql默认的隔离级别为Repeatable Read,因此只会出现幻读的情况。
--下面的三个性能视图分别对应到不同的级别
SQL> 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
1).会话级别执行环境(视图v$ses_optimizer_env)
--oracle视图v$ses_optimizer_env,也叫做会话优化器环境视图,可以用来查看会话优化器使用的参数,包括本次会话使用的特定环境声明和系统优化器参数环境总览。
--v$ses_optimizer_env用来查看每个会话的优化器环境,可以针对某个会话查看其环境变量的设置.该视图显示了每个会话被设置的优化器参数相关的信息.
select * from v$SES_OPTIMIZER_ENV where name ='transaction_isolation_level';
SQL> select * from v$SES_OPTIMIZER_ENV
where name ='transaction_isolation_level';
SID ID NAME SQL_FEATURE ISD VALUE CON_ID
----- --- ---------------------------- --------------- --- ------------------------- ----------
1 218 transaction_isolation_level QKSFM_ALL YES read_commited 1
2 218 transaction_isolation_level QKSFM_ALL YES read_commited 1
3 218 transaction_isolation_level QKSFM_ALL YES read_commited 1
4 218 transaction_isolation_level QKSFM_ALL YES read_commited 1
.
.
.
105 rows selected.
2).实例级别执行环境(视图v$sys_optimizer_env)
select * from V$SYS_OPTIMIZER_ENV where name ='transaction_isolation_level';
SQL> select * from V$SYS_OPTIMIZER_ENV where name ='transaction_isolation_level';
ID NAME SQL_FEATURE ISD VALUE DEFAULT_VALUE CON_ID
--- ---------------------------- ----------- --- ---------------- -------------- ------
218 transaction_isolation_level QKSFM_ALL YES read_commited read_commited 1
SQL>
3).语句级别执行环境(视图v$sql_optimizer_env)
select * from V$SQL_OPTIMIZER_ENV where name ='transaction_isolation_level';
ADDRESS HASH_VALUE SQL_ID CHILD_ADDRESS CHILD_NUMBER ID NAME ISD VALUE CON_ID
---------------- ---------- ------------- ---------------- ------------ ---- ------------------------------ --- -------------- ------
0000000077E8CA10 1079377382 3s1yukp05bzg6 0000000077E8B2B8 0 218 transaction_isolation_level YES read_commited 1
000000008065E4D0 1746927093 8vr9hwjn1zzgp 0000000079469950 1 218 transaction_isolation_level YES read_commited 3
000000008065E4D0 1746927093 8vr9hwjn1zzgp 000000008065CD78 0 218 transaction_isolation_level YES read_commited 1
000000007BAB00C0 3945791050 cv6zspbpkzzka 000000007B79BF70 1 218 transaction_isolation_level YES read_commited 3
000000007BAB00C0 3945791050 cv6zspbpkzzka 000000007BAAE968 0 218 transaction_isolation_level YES read_commited 1
00000000747082D8 4262199125 aca4xvmz0rzup 00000000746FD1D0 1 218 transaction_isolation_level YES read_commited 1
00000000747082D8 4262199125 aca4xvmz0rzup 0000000074706B80 0 218 transaction_isolation_level YES read_commited 1
00000000746B4640 1375207257 062savj8zgzut 00000000746B2EE8 0 218 transaction_isolation_level YES read_commited 1
.
.
.
2351 rows selected.
SQL>
===========================================================================================
https://blog.csdn.net/heianemo/article/details/7930198
使用优化器性能视图获取SQL语句执行环境
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
SQL> 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$sys_optimizer_env)
--提供实例级别的环境执行的信息,Oracle优化器在为SQL语句生成执行计划时,会根据实例级别参数的值来确定,如 optimizer_mode用于确定优化器的模式,optimizer_index_cost_adj用于确定全表扫描与索引扫描之间成本开销的比值等
实例级别的参数可以使用下面的方式来设置:
alter system set parameter=value scope=memory | both |spfile;
--我们来看看当前实例级别的运行环境
SQL> select
name,
value,
isdefault
from
v$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,因此应当慎重.当然,如果某个参数设置的不合理,其影响也是全局的,因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因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$ses_optimizer_env) --三个参数:cursor_sharing,optimizer_mode,db_file_multiblock_read_count限制
--与实例级别相对应的会话级别视图是v$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.
SQL> show parameter cursor_shar
NAME |TYPE |VALUE
------------------------------------|-----------|------------------
cursor_sharing |string |EXACT
SQL> alter session set cursor_sharing=force;
Session altered.
SQL> show parameter cursor_shar
NAME |TYPE |VALUE
------------------------------------|-----------|------------------
cursor_sharing |string |FORCE
SQL> alter session set optimizer_mode=first_rows_100;
Session altered.
SQL> show parameter optimizer_mode
NAME |TYPE |VALUE
------------------------------------|--------------------------------|--------------------
optimizer_mode |string |FIRST_ROWS_100
SQL> alter session set db_file_multiblock_read_count=128;
Session altered.
SQL> select username,sid,serial# from v$session where username='SCOTT';
USERNAME | SID| SERIAL#
------------------------------|----------|----------
SCOTT | 159| 5
SQL> select name,value,isdefault
from v$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) '参数optimizer_index_cost_adj和cursor_sharing限制'
--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.因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。
SQL> select /*+ no_hint */ ename,job,sal from emp where empno=7369; -->此SQL语句会根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,-此时的no_hint不是一个有效的提示,被当成注释
ENAME |JOB | SAL
----------|---------|----------
Henry |CLERK | 1400
SQL> select /*+ all_rows */ 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,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
ENAME |JOB | SAL
----------|---------|----------
Henry |CLERK | 1400
SQL> show parameter optimizer_index_cost_adj -->查看参数设置
NAME |TYPE |VALUE
------------------------------------|-----------|------------------------------
optimizer_index_cost_adj |integer |100
SQL> show parameter cursor_sharing -->查看参数设置
NAME |TYPE |VALUE
------------------------------------|-----------|------------------------------
cursor_sharing |string |EXACT
SQL> select avg(sal) from emp; -->聚合运算
AVG(SAL)
----------
2335
SQL> alter session set cursor_sharing=force; -->基于session级别修改参数
Session altered.
SQL> alter session set optimizer_index_cost_adj=80; -->基于session级别修改参数
Session altered.
SQL> 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
SQL> 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语句父游标与子游标执行环境不同的地方
SQL> 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
-->看到父游标与子游标的信息全部被列出来
SQL> select address, name, value, isdefault,child_number
2 from v$sql_optimizer_env
3 where sql_id = '5du23va3p3ad0'
4 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://blog.csdn.net/robinson_0612
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.
===========================================================================================