[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,或者讲遇到的问题很少.
--//抽一点点时间,简单探究12c Top Frequency histogram.
--//以前的频率直方图Frequency histogram,受限bucket(桶的大小),如果有255个不同值,oracle分析后不会建立频率直方图,而是建立高
--//度直方图.这样的情况会导致一些流行值的统计在显示执行计划时差距很大.而12c引入了Top Frequency histogram,注意这里的top,
--//我的理解就是流行值(popular),也就是这样建立的直方图仅仅包括popular,其他non-popular不考虑,这样在sql语句的查询这些
--//popular时,显示的统计信息相对准确,从而有利于oracle选择正确的执行计划.
--//以下是我的学习笔记,也许会存在许多错误,仅仅做一个记录.我也看了许多别人的blog.^_^.而且我目前的环境只有12.0.0.1(版本太
--//低).
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)
--//翻译过来NDV(也就是字段的不同值)大于N(指bucket的数量).
--//流行值(popular)在Top-frequent中合计数量/总计数量之比要大于(1-(1/n)*100).如果建立10个桶,这样流行值的总计必须在90%以上
2.首先验证(1-(1/n)*100)比值是否正确:
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
--//如果加入条件where round(n3/n2,5) >round(1-1/rownum,5),全部输出.也就是这样如果桶小于32,大于1.建立的都是Top Frequency.
3.继续测试:
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).
4.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
--//DENSITY=1/SAMPLE_SIZE/2, 1/14600/2=.00003424657534246575正好符合.
5.现在看看执行计划:
SCOTT@test01p> select count(*) from t where owner='DVSYS';
COUNT(*)
----------
352
SCOTT@test01p> @ dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID 2at34f0zaqhzj, child number 0
-------------------------------------
select count(*) from t where owner='DVSYS'
Plan hash value: 2966233522
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 428 (100)| | 1 |00:00:00.01 | 1544 |
| 1 | SORT AGGREGATE | | 1 | 1 | 8 | | | 1 |00:00:00.01 | 1544 |
|* 2 | TABLE ACCESS FULL| T | 1 | 352 | 2816 | 428 (0)| 00:00:01 | 352 |00:00:00.01 | 1544 |
---------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
2 - SEL$1 / T@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("OWNER"='DVSYS')
--//可以发现e_rows=A-Rows.可以发现非常准确.
--//查看直方图信息.
SCOTT@test01p> select endpoint_number,endpoint_actual_value from user_tab_histograms where table_name ='T' and column_name ='OWNER' order by 1;
ENDPOINT_NUMBER ENDPOINT_ACTUAL_VALU
--------------- --------------------
3405 APEX_040200
3810 CTXSYS
4162 DVSYS
5981 MDSYS
9138 ORDSYS
10185 PUBLIC
11127 SYS
11768 SYSTEM
12155 WMSYS
13140 XDB
10 rows selected.
--//4162-3810=352,可以发现正好符合.也就是popular值统计很正确.看看非popular值.
SCOTT@test01p> select count(*) from t where owner='DVSYS1';
COUNT(*)
----------
0
Plan hash value: 2966233522
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 428 (100)| | 1 |00:00:00.01 | 1544 |
| 1 | SORT AGGREGATE | | 1 | 1 | 8 | | | 1 |00:00:00.01 | 1544 |
|* 2 | TABLE ACCESS FULL| T | 1 | 66 | 528 | 428 (0)| 00:00:01 | 0 |00:00:00.01 | 1544 |
---------------------------------------------------------------------------------------------------------------------
SCOTT@test01p> select count(*) from t where owner='SCOTT';
COUNT(*)
----------
96
Plan hash value: 2966233522
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 428 (100)| | 1 |00:00:00.01 | 1544 |
| 1 | SORT AGGREGATE | | 1 | 1 | 8 | | | 1 |00:00:00.01 | 1544 |
|* 2 | TABLE ACCESS FULL| T | 1 | 66 | 528 | 428 (0)| 00:00:01 | 96 |00:00:00.01 | 1544 |
---------------------------------------------------------------------------------------------------------------------
--//可以发现估计E-Rows如何计算的呢?
6.做10053跟踪:
D:\tools\sqllaji>cat 10053x.sql
execute dbms_sqldiag.dump_trace(p_sql_id=>'&1',p_child_number=>&2,p_component=>'Compiler',p_file_id=>'&&1');
SCOTT@test01p> @ 10053x f31kz63ksu1tc 0
PL/SQL procedure successfully completed.
***************************************
SINGLE TABLE ACCESS PATH
Single Table Cardinality Estimation for T[T]
SPD: Return code in qosdDSDirSetup: NOCTX, estType = TABLE
Column (#1):
NewDensity:0.004545, OldDensity:0.000034 BktCnt:13140.000000, PopBktCnt:13140.000000, PopValCnt:10, NDV:32
Column (#1): OWNER(VARCHAR2)
AvgLen: 8 NDV: 32 Nulls: 0 Density: 0.000000
Histogram: Top-Freq #Bkts: 13140 UncompBkts: 13140 EndPtVals: 10 ActualVal: yes
Table: T Alias: T
Card: Original: 14600.000000 Rounded: 66 Computed: 66.36 Non Adjusted: 66.36
Access Path: TableScan
Cost: 428.36 Resp: 428.36 Degree: 0
Cost_io: 428.00 Cost_cpu: 14122025
Resp_io: 428.00 Resp_cpu: 14122025
Best:: AccessPath: TableScan
Cost: 428.36 Degree: 1 Resp: 428.36 Card: 66.36 Bytes: 0
check parallelism for statement[<unnamed>]
kkfdtParallel: parallel is possible (no statement type restrictions)
kkfdPaForcePrm: dop:1 ()
use dictionary DOP(1) on table
kkfdPaPrm:- The table : 106380
kkfdPaPrm:DOP = 1 (computed from hint/dictionary/autodop)
kkfdiPaPrm: dop:1 serial(?)
***************************************
--//使用 NewDensity:0.004545.
BktCnt:13140.000000, PopBktCnt:13140.000000 => 对应就是前10个流行值的总和.
--//非流行值的数量: 14600-13140=1460
--//非流行值的桶数量: 32-10=22
--//非流行值的数量/非流行值的桶数量 1460/22=66.36363636363636363636,四舍五入66,正好符合执行计划的推断.
--//NewDensity的计算 =1460/14600/22=.00454545454545454545,非常接近.
---恢复内容结束---
[20170603]12c Top Frequency histogram.txt的更多相关文章
- [20170604]12c Top Frequency histogram补充.txt
[20170604]12c Top Frequency histogram补充.txt 1.环境:SCOTT@test01p> @ ver1PORT_STRING ...
- [20181105]再论12c set feedback only.txt
[20181105]再论12c set feedback only.txt --//前一阵子的测试,链接:http://blog.itpub.net/267265/viewspace-2216290/ ...
- [20181015]12C SQL Translation Framework.txt
[20181015]12C SQL Translation Framework.txt --//12c提供一个dba改写sql语句的可能性,实际上10g,11g之前也有一个包DBMS_ADVANCED ...
- [20180914]oracle 12c 表 full_hash_value如何计算.txt
[20180914]oracle 12c 表 full_hash_value如何计算.txt --//昨天在12c下看表full_hash_value与11g的full_hash_value不同,不过 ...
- oracle 12c AUTO_SAMPLE_SIZE动态采用工作机制
The ESTIMATE_PERCENT parameter in DBMS_STATS.GATHER_*_STATS procedures controls the percentage of ro ...
- 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 ...
- oracle 12c直方图收集的增强
在oracle 12c之前,收集直方图信息是相对比较耗费资源的,因为要重复扫描几次:在oracle 12c中,则有较大的提升,具体可参考https://jonathanlewis.wordpress. ...
- 定制保存top输出信息的格式详解
top命令的重要性和使用方法不多说了,这里终点讨论如何保存top命令的输出信息. 保存top命令的输出到一个文件的方法是:top -n1b > topinfo.txt,这没什么好奇的,但 ...
- [20191127]表 full Hash Value的计算.txt
[20191127]表 full Hash Value的计算.txt --//曾经做过表full Hash Value的计算,当时我是通过建立简单的schema以及表名的形式,使用hashcat破解o ...
随机推荐
- centos7编译linux的内核源码
昨天编译了一个linux 内核源码,遇到一些问题, 今天把我遇到的问题和解决方法分享给大家.希望可以帮助到需要的人. 1.检查是否安装了相应的包 我第一次编译的时候只安装的“Development T ...
- ES6躬行记（10）——正则表达式
在ES5中,如果使用构造函数RegExp()初始化RegExp对象(即正则表达式),并且它的第一个参数是正则表达式时,那么不允许再传入标志字符串(即第二个参数).而ES6更改了这项限制,如果传入了第二 ...
- vue中使用refs定位dom出现undefined？
之前在公司做项目,一直感觉用ref来定位dom节点挺方便的.但是期间遇到了一个问题,就是在mounted(){}钩子里面使用this.$refs.xxx,打印出来的却是undefined? 于是我就对 ...
- 面试题·HashMap和Hashtable的区别(转载再整理)
原文链接: Javarevisited 翻译: ImportNew.com- 唐小娟 译文链接: http://www.importnew.com/7010.html HashMap和Hashtabl ...
- QT 设置有效绘图区域
void QPainter::setClipRect(int x, int y, int width, int height, Qt::ClipOperation operation = Qt::Re ...
- Linux某些命令找不到/无法使用
1.zip/unzip: command not found yum list | grep zip/unzip yum install zip yum install unzip 2.rz -y/s ...
- 大话DI依赖注入+IOC控制反转（二） 之 浅析.Net Core中的DI与IOC
转发时请注明原创作者及地址,否则追究责任.原创:alunchen 在上一篇文章中,我们聊了很多关于定义的方面,比较孤燥,下面我们结合.Net Core聊一下依赖注入&控制反转. 三种对象生 ...
- 一个简单的Code First建立
1]从VS中建立一个mvc程序 记得添加NuGet包 然后在web.config中添加链接数据库的语句 <connectionStrings> <add name="Ent ...
- CLR via c# 值类型“不可变”
昨天看书看到引用类型和值类型,书中讲到值类型“不可变”,如图: 看了两遍没怎么看懂,又仔细多看了几遍,说下我的理解: 比如说一个int类型有几个成员, MaxValue.MinValue的值是不可变的 ...
- MySQL分页查询性能优化
当需要从数据库查询的表有上万条记录的时候,一次性查询所有结果会变得很慢,特别是随着数据量的增加特别明显,这时需要使用分页查询.对于数据库分页查询,也有很多种方法和优化的点.下面简单说一下我知道的一些方 ...