[20170604]12c Top Frequency histogram补充.txt

1.环境:
SCOTT@test01p> @　ver1
PORT_STRING                    VERSION        BANNER                                                                               CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0           12.1.0.1.0     Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production              0

--//如果要建立Top Frequency histogram必须要满足几个条件:
--//链接 raajeshwaran.blogspot.co.id/2016/06/top-frequency-histogram-in-12c.html

The database creates a Top frequency histogram, when the following criteria are met.

NDV is greater than n, where n is the requested number of buckets (default 254)
The percentage of rows occupied by Top-frequent values is greater than or equal to the threshold p where p is (1-(1/n)*100).
The estimate_percent parameter in dbms_stats gathering procedure should be auto_sample_size (set to default)

SCOTT@test01p> create table t as select * from dba_objects;
Table created.

select column_name,num_distinct,density,histogram,SAMPLE_SIZE
  from user_tab_col_statistics
  where table_name ='T'
  and column_name ='OWNER';

COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32     .03125 NONE                  91695

--//12c ctas 建立统计信息,但是不会建立直方图.density 1/32=.03125.
SCOTT@test01p> select count(*) from t;
  COUNT(*)
----------
     91695

--//随手写的sql语句:
with a as (select distinct owner,count(*) over(partition by owner) n1 ,count(*) over () n2 from t order by 2 desc ),
b as (select owner,n1,n2,sum(n1) over (order by n1 desc) n3  from a order by n1 desc)
select rownum,owner,n1,n2,n3,round(n3/n2,5) x1,round(1-1/rownum,5) x2 from b;

ROWNUM OWNER                N1         N2         N3         X1         X2
------ ----------------- ----- ---------- ---------- ---------- ----------
     1 SYS               41942      91695      41942     .45741          0
     2 PUBLIC            37142      91695      79084     .86247         .5
     3 APEX_040200        3405      91695      82489      .8996     .66667
     4 ORDSYS             3157      91695      85646     .93403        .75
     5 MDSYS              1819      91695      87465     .95387         .8
     6 XDB                 985      91695      88450     .96461     .83333
     7 SYSTEM              641      91695      89091      .9716     .85714
     8 CTXSYS              405      91695      89496     .97602       .875
     9 WMSYS               387      91695      89883     .98024     .88889
    10 DVSYS               352      91695      90235     .98408         .9
    11 SH                  309      91695      90544     .98745     .90909
    12 ORDDATA             292      91695      90836     .99063     .91667
    13 LBACSYS             209      91695      91045     .99291     .92308
    14 OE                  142      91695      91187     .99446     .92857
    15 SCOTT                96      91695      91283     .99551     .93333
    16 GSMADMIN_INTERNAL    77      91695      91360     .99635      .9375
    17 IX                   58      91695      91418     .99698     .94118
    18 DBSNMP               55      91695      91473     .99758     .94444
    19 PM                   44      91695      91517     .99806     .94737
    20 HR                   35      91695      91552     .99844        .95
    21 OLAPSYS              25      91695      91577     .99871     .95238
    22 OJVMSYS              23      91695      91600     .99896     .95455
    23 DVF                  19      91695      91619     .99917     .95652
    24 FLOWS_FILES          13      91695      91632     .99931     .95833
    25 AUDSYS               12      91695      91644     .99944        .96
    26 ORDPLUGINS           10      91695      91664     .99966     .96154
    27 OUTLN                10      91695      91664     .99966     .96296
    28 BI                    8      91695      91688     .99992     .96429
    29 ORACLE_OCM            8      91695      91688     .99992     .96552
    30 SI_INFORMTN_SCHEM     8      91695      91688     .99992     .96667
    31 APPQOSSYS             5      91695      91693     .99998     .96774
    32 TEST                  2      91695      91695          1     .96875

D:\temp>cat a1.sql
cat a1.sql
exec  dbms_stats.gather_table_stats(ownname=>user,tabname=>'T',method_opt=>'for columns owner size &1');
select column_name,num_distinct,density,histogram,SAMPLE_SIZE from user_tab_col_statistics where table_name ='T' and column_name ='OWNER';

SCOTT@test01p> @ a1.sql 2
PL/SQL procedure successfully completed.

COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32     .03125 HYBRID                 5500

SCOTT@test01p> @ a1.sql 3
PL/SQL procedure successfully completed.

COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 5.4529E-06 TOP-FREQUENCY         91695

SCOTT@test01p> @ a1.sql 4
PL/SQL procedure successfully completed.

COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 5.4529E-06 TOP-FREQUENCY         91695

SCOTT@test01p> @ a1.sql 31
PL/SQL procedure successfully completed.
COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 5.4529E-06 TOP-FREQUENCY         91695

SCOTT@test01p> @ a1.sql 32
PL/SQL procedure successfully completed.

COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 5.4529E-06 FREQUENCY             91695

--//除了bucket=2,32建立的直方图HYBRID,FREQUENCY外,建立的都是TOP-FREQUENCY.
--//以10个bucket为例.解方程式(90235-x)/(91695-x)=0.9 ,得到x=77095.也就是要减少77095.

--//delete t where owner='SYS' and rownum<=41000;
--//delete t where owner='PUBLIC' and rownum<=36095;

SCOTT@test01p> delete t where owner='SYS' and rownum<=41000;
41000 rows deleted.

SCOTT@test01p> delete t where owner='PUBLIC' and rownum<=36095;
36095 rows deleted.

SCOTT@test01p> commit ;
Commit complete.

with a as (select distinct owner,count(*) over(partition by owner) n1 ,count(*) over () n2 from t order by 2 desc ),
b as (select owner,n1,n2,sum(n1) over (order by n1 desc) n3  from a order by n1 desc)
select rownum,owner,n1,n2,n3,round(n3/n2,5) x1,round(1-1/rownum,5) x2 from b where rownum<=11;

ROWNUM OWNER         N1         N2         N3         X1         X2
------ ----------- ---- ---------- ---------- ---------- ----------
     1 APEX_040200 3405      14600       3405     .23322          0
     2 ORDSYS      3157      14600       6562     .44945         .5
     3 MDSYS       1819      14600       8381     .57404     .66667
     4 PUBLIC      1047      14600       9428     .64575        .75
     5 XDB          985      14600      10413     .71322         .8
     6 SYS          942      14600      11355     .77774     .83333
     7 SYSTEM       641      14600      11996     .82164     .85714
     8 CTXSYS       405      14600      12401     .84938       .875
     9 WMSYS        387      14600      12788     .87589     .88889
    10 DVSYS        352      14600      13140         .9         .9
    11 SH           309      14600      13449     .92116     .90909
11 rows selected.
--//backet=10,前面10个值占90%.

SCOTT@test01p> @ a1 10
PL/SQL procedure successfully completed.
COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 .000034247 TOP-FREQUENCY         14600

--//再减少1条记录.
SCOTT@test01p> delete t where owner='SYS' and rownum<=1;
1 row deleted.

SCOTT@test01p> commit ;
Commit complete.

ROWNUM OWNER         N1         N2         N3         X1         X2
------ ----------- ---- ---------- ---------- ---------- ----------
     1 APEX_040200 3405      14599       3405     .23324          0
     2 ORDSYS      3157      14599       6562     .44948         .5
     3 MDSYS       1819      14599       8381     .57408     .66667
     4 PUBLIC      1047      14599       9428      .6458        .75
     5 XDB          985      14599      10413     .71327         .8
     6 SYS          941      14599      11354     .77772     .83333
     7 SYSTEM       641      14599      11995     .82163     .85714
     8 CTXSYS       405      14599      12400     .84937       .875
     9 WMSYS        387      14599      12787     .87588     .88889
    10 DVSYS        352      14599      13139     .89999         .9
    11 SH           309      14599      13448     .92116     .90909
11 rows selected.
--//现在前10占.89999.

SCOTT@test01p> @ a1 10
PL/SQL procedure successfully completed.

COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32    .018378 HYBRID                14599

--//可以发现建立的直方图不是TOP-FREQUENCY,而是HYBRID(混合型直方图).
--//转化成TOP-FREQUENCY.
SCOTT@test01p> insert into t  select * from dba_objects where owner='SYS' and rownum=1;
1 row created.

SCOTT@test01p> commit ;
Commit complete.

SCOTT@test01p> @ a1 10
PL/SQL procedure successfully completed.

COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 .000034247 TOP-FREQUENCY         14600

--//以上内容是昨天的测试.
--//前面我提到如果取样不是auto_sample_size,也可能不行,测试看看.

2.取样大小Estimate_Percent  => NULL.
SCOTT@test01p> exec  dbms_stats.gather_table_stats(ownname=>user,tabname=>'T',method_opt=>'for columns owner size 10',Estimate_Percent  => NULL);
PL/SQL procedure successfully completed.

SCOTT@test01p> select column_name,num_distinct,density,histogram,SAMPLE_SIZE from user_tab_col_statistics where table_name ='T' and column_name ='OWNER';
COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32    .018379 HYBRID                14600

--//可以发现如果全取样,反而生成混合型直方图.

3.取样大小Estimate_Percent  => SYS.DBMS_STATS.AUTO_SAMPLE_SIZE,Block_sample => TRUE.
SCOTT@test01p> exec  dbms_stats.gather_table_stats(ownname=>user,tabname=>'T',method_opt=>'for columns owner size 10',Estimate_Percent  => SYS.DBMS_STATS.AUTO_SAMPLE_SIZE,Block_sample => TRUE);
PL/SQL procedure successfully completed.

SCOTT@test01p> select column_name,num_distinct,density,histogram,SAMPLE_SIZE from user_tab_col_statistics where table_name ='T' and column_name ='OWNER';
COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 .000034247 TOP-FREQUENCY         14600

--//可以发现Estimate_Percent=>SYS.DBMS_STATS.AUTO_SAMPLE_SIZE,不管是块取样依旧.

4.取样Estimate_Percent  => 100,90看看.
SCOTT@test01p> exec  dbms_stats.gather_table_stats(ownname=>user,tabname=>'T',method_opt=>'for columns owner size 10',Estimate_Percent  => 100);
PL/SQL procedure successfully completed.

SCOTT@test01p> select column_name,num_distinct,density,histogram,SAMPLE_SIZE from user_tab_col_statistics where table_name ='T' and column_name ='OWNER';
COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 .062908991 HEIGHT BALANCED       14600

SCOTT@test01p> exec  dbms_stats.gather_table_stats(ownname=>user,tabname=>'T',method_opt=>'for columns owner size 10',Estimate_Percent  => 90);
PL/SQL procedure successfully completed.

SCOTT@test01p> select column_name,num_distinct,density,histogram,SAMPLE_SIZE from user_tab_col_statistics where table_name ='T' and column_name ='OWNER';
COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32      .0625 HEIGHT BALANCED       13108

--//看来仅仅Estimate_Percent  => SYS.DBMS_STATS.AUTO_SAMPLE_SIZE才会生成TOP-FREQUENCY直方图.
SCOTT@test01p> exec  dbms_stats.gather_table_stats(ownname=>user,tabname=>'T',method_opt=>'for columns owner size 10',Estimate_Percent  => SYS.DBMS_STATS.AUTO_SAMPLE_SIZE);
PL/SQL procedure successfully completed.

SCOTT@test01p> select column_name,num_distinct,density,histogram,SAMPLE_SIZE from user_tab_col_statistics where table_name ='T' and column_name ='OWNER';
COLUMN_NAME          NUM_DISTINCT    DENSITY HISTOGRAM       SAMPLE_SIZE
-------------------- ------------ ---------- --------------- -----------
OWNER                          32 .000034247 TOP-FREQUENCY         14600

--//有机会研究HYBRID直方图.

[20170604]12c Top Frequency histogram补充.txt的更多相关文章

  1. [20170603]12c Top Frequency histogram.txt

    ---恢复内容开始--- [20170603]12c Top Frequency histogram.txt --//个人对直方图了解很少,以前2种直方图类型对于目前的许多应用来讲已经足够,或者讲遇到 ...

  2. [20180928]ora-01426(补充).txt

    [20180928]ora-01426(补充).txt --//链接:http://www.itpub.net/thread-2105458-1-1.html--//做一点点必要的补充: 1.环境:S ...

  3. [20170916]sqlplus set array最小2补充.txt

    [20170916]sqlplus set array最小2补充.txt --//以前写的贴子,链接http://blog.itpub.net/267265/viewspace-1453652/--/ ...

  4. [20190312]关于增量检查点的疑问(补充).txt

    [20190312]关于增量检查点的疑问(补充).txt --//有人问我以前写一个帖子的问题,关于增量检查点的问题,链接如下:http://blog.itpub.net/267265/viewspa ...

  5. [20190214]11g Query Result Cache RC Latches补充.txt

    [20190214]11g Query Result Cache RC Latches补充.txt --//上午测试链接:http://blog.itpub.net/267265/viewspace- ...

  6. [20181108]12c sqlplus rowfetch参数4.txt

    [20181108]12c sqlplus rowfetch参数4.txt --//12cR2 可以改变缺省rowfetch参数.11g之前缺省是1.通过一些测试说明问题.--//前几天做的测试有点乱 ...

  7. [20181031]12c 在线移动数据文件.txt

    [20181031]12c 在线移动数据文件.txt --//12c以前,移动或者改名数据文件是一项比较麻烦的事情,至少要停一下业务.而12c支持在线移动或者改名数据文件,并且有点不可思议--//的是 ...

  8. [20171107]dbms_shared_pool.pin补充.txt

    [20171107]dbms_shared_pool.pin补充.txt --//上午的测试,做一些补充,主要还是一些理解问题. 1.环境:SCOTT@book> @ &r/ver1 P ...

  9. top 自动执行的shell脚本中，使用top -n 1 > log.txt, 上电自动执行，文件无输出

    . 自动执行的shell脚本中,使用top -n > log.txt, 上电自动执行,文件无输出,使用一下命令解决: //usr/bin/top -d -n -b > log.txt 如果 ...

随机推荐

  1. 第一个NHibernateDemo

    什么是Nhibernate,Nhibernate是一个面向.Net环境的对 象/关系数据库映射工具.(ORM) 1.搭建项目基本框架: (1)创建MVC项目,命名为NHShop.Web. (2)依次分 ...

  2. Oracle性能优化之查询语句通用原则

    作者早期文章 Oracle优化 索引是表的一个概念部分 , 用来提高检索数据的效率, ORACLE 使用了一个复杂的自平衡 B-tree 结构 . 通常 , 通过索引查询数据比全表扫描要快 . 当 O ...

  3. 高性能Mysql笔记 — 优化

    性能优化 了解查询的整个生命周期,清楚每个阶段的时间消耗情况 性能分析 慢查询日志--服务器性能分析 参考 慢查询日志是优化很重要的手段,但是开启慢查询日志对性能的影响并不大,所以可以考虑在线上打开慢 ...

  4. Go基础系列：接口类型断言和type-switch

    接口类型探测:类型断言 接口实例中存储了实现接口的类型实例,类型的实例有两种:值类型实例和指针类型实例.在程序运行过程中,接口实例存储的实例类型可能会动态改变.例如: // ins是接口实例 var ...

  5. MySQL系列详解十：MySQL多源复制演示-技术流ken

    前言 多源复制即多主一从结构,多个主服务器端的数据都会同步到后端一个从服务器上面.至于为什么要做多源复制下面的总结很到位. 1.灾备作用:将各个库汇总在一起,就算是其他库都挂了(整个机房都无法连接了) ...

  6. 前端（一）之 HTML

    前端之 HTML 前言 python 基础.网络编程.并发编程与数据库要开始告一段落了,从现在开始进入前端的学习.前端的东西多且杂,需要好好地练习. 什么是前端 前端即网站前台部分,运行在 PC 端, ...

  7. 匿名函数python内置高阶函数以及递归

    匿名函数 python定义一个函数通常使用def关键词,后面跟函数名,然后是注释.代码块等. def func(): '''注释''' print('from func') 这样就在全局命名空间定义了 ...

  8. tomcat编译项目后，classes文件没有相应的改变；

    tomcat编译项目后,classes文件没有相应的改变: tomcat不能将项目部署到服务器: 1.首先,在tomcat安装目录webapps中将编译后的整个项目删掉,然后再在eclipse将tom ...

  9. SVN、CVS、VSS区别

    废话不多说,撸起袖子敲黑板 !~~ #首先向大家简要描述一下SVN与CVS.VSS的介绍与对比: 介绍: 三种都是版本控制软件, 多数用于源代码管理1.CVS(Concurrent Version S ...

  10. spring_04bean的生命周期

    一.前言 spring框架中的bean对象生命周期是面试时常考的问题 往往笔试,面试总喜欢问生命周期的问题 二.spring_bean应用上下文生命周期图: 三.生命周期流程(bean应用上下文): ...