[20180730]exadata与行链接.txt

--//最近一段时间在看<expert oracle exadata>,智能扫描的三大优化方法是:字段投影,谓词过滤,存储索引.大多数智能扫描
--//优化方法的主要目标就是在执行扫描时减少需要传输回数据块服务端的数据量.
--//而智能扫描的先决条件,满足三个基本条件:
--//1.必须要是对象上的全扫描.
--//2.扫描必须要使用oracle直接路径读取机制.
--//3.对象必须存储在exadata存储中.

--//有几种情况转换为块传输模式:
--//1.一致性读取,
--//2,行链接(注意:不是行迁移)
--//3.存储服务器CPU太忙.

--//正好生产系统有1张大表存在大量行链接.自己测试看看.

1.环境:
xxxx> @ &r/ver1

PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

2.测试:
xxxx> select bytes/1024/1024/1024 GB ,BLOCKS from dba_segments where owner='XXXX_YYY' and segment_name='BIG_TAB';
        GB     BLOCKS
---------- ----------
207.549805   27203968

--//表占用207G.
xxxx> set timing on
xxxx> @ &r/viewsess 'table fetch continued row'
NAME                       STATISTIC#      VALUE        SID
-------------------------- ---------- ---------- ----------
table fetch continued row         417          0       2323

Elapsed: 00:00:00.00
xxxx> select /*+ full(a) */ count(*) from xxxxxx_yyy.big_tab a;
  COUNT(*)
----------
  44669678

Elapsed: 00:01:38.73
xxxx> @ &r/viewsess 'table fetch continued row'
NAME                      STATISTIC#      VALUE        SID
------------------------- ---------- ---------- ----------
table fetch continued row        417          0       2323
Elapsed: 00:00:00.01

--//需要大约98秒完成查询.table fetch continued row的记数没有变化.

xxxx> @ &r/desc xxxxxx_yyy.big_tab;
Name          Null?    Type
------------- -------- ----------------------------
YZBXH         NOT NULL NUMBER(18)
BRID          NOT NULL NUMBER(18)
ZYH           NOT NULL NUMBER(18)
YEPB          NOT NULL NUMBER(1)
BRKS          NOT NULL NUMBER(4)
BRBQ                   NUMBER(4)
BRCH                   VARCHAR2(20)
YDYZLB        NOT NULL NUMBER(4)
XMLB          NOT NULL NUMBER(8)
...
CAKEY                  VARCHAR2(2000)
YZCA                   VARCHAR2(3000)
TZ_CAKEY               VARCHAR2(2000)
TZCA                   VARCHAR2(3000)
HSCAKEY                VARCHAR2(2000)
HSCA                   VARCHAR2(3000)
TZ_HSCAKEY             VARCHAR2(2000)
TZ_HSCA                VARCHAR2(3000)
DYSJ                   DATE
YZZXSJ                 VARCHAR2(80)
ZXTZSJ                 DATE
ZYDY                   NUMBER(1)
FZLJ                   NUMBER(8)
BRZH                   NUMBER(8)
TZBRZH                 NUMBER(8)
TJSJ                   DATE
TQMXBZ                 NUMBER(1)

--//顺便找靠前的可以为NULL的字段BRBQ. 注意看那些XXkey的字段,正是这些字段导致了大量的行链接与行迁移.

xxxx> select sysdate from dual;
SYSDATE
-------------------
2018-07-30 08:49:54

Elapsed: 00:00:00.01
xxxx> select /*+ full(a) */ count(BRBQ) from xxxxxx_yyy.big_tab a;
select /*+ full(a) */ count(BRBQ) from xxxxxx_yyy.big_tab a
                                                  *
ERROR at line 1:
ORA-01013: user requested cancel of current operation
Elapsed: 00:03:09.84

xxxx> select sysdate from dual;
SYSDATE
-------------------
2018-07-30 08:53:37

Elapsed: 00:00:00.00
xxxx> @ &r/viewsess 'table fetch continued row'
NAME                      STATISTIC#      VALUE        SID
------------------------- ---------- ---------- ----------
table fetch continued row        417      53476       2323
Elapsed: 00:00:00.00

--//时间太长仅仅测试不到4分钟,放弃!!(注上个星期测试4个小时也没有出来报ora-01555错误,当时选择靠后的字段).说明可以大量的行
--//链接导致无法充分发挥exadata智能扫描的优势,转为块传输模式.

--//如果在服务器上观察可以发现:
# perf top -k /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
   PerfTop:    5431 irqs/sec  kernel:51.3%  exact:  0.0% [1000Hz cycles],  (all, 24 CPUs)
----------------------------------------------------------------------------------------------------------

samples  pcnt function                DSO
             _______ _____ _______________________ _______________________________________________________

1125.00  5.3% kafger                  /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
              763.00  3.6% qertbFetchByRowID       /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
                           ~~~~~~~~~~~~~~~~  
              740.00  3.5% kafgex1                 /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
              740.00  3.5% kcbgtcr                 /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
              607.00  2.8% kdifxs1                 /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
              477.00  2.2% qerixtFetch             /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
              451.00  2.1% expepr                  /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle
              386.00  1.8% kdsgrp                  /u01/app/oracle/product/11.2.0.4/dbhome_1/bin/oracle

--//出现许多qertbFetchByRowID函数调用.

3.顺便测试exadata的存储索引:
--//重新登录:
xxxx> @ &r/viewsess 'storage'
NAME                                                                   STATISTIC#      VALUE        SID
---------------------------------------------------------------------- ---------- ---------- ----------
cell physical IO bytes saved by storage index                                 274          0       4821

xxxx> @ &r/viewsess 'table fetch continued row'
NAME                                                                   STATISTIC#      VALUE        SID
---------------------------------------------------------------------- ---------- ---------- ----------
table fetch continued row                                                     417          0       4821

xxxx> set timing on
xxxx> select /*+ full(a) */ count(*) from xxxxxx_yyy.big_tab a where ZXTZSJ between trunc(sysdate)-1 and trunc(sysdate)-1+1/86400;
  COUNT(*)
----------
         5
Elapsed: 00:47:05.16
--//仅仅取1秒的日期范围数据,竟然需要47分钟.

xxxx> @ &r/viewsess 'table fetch continued row'
NAME                                                                   STATISTIC#      VALUE        SID
---------------------------------------------------------------------- ---------- ---------- ----------
table fetch continued row                                                     417    3461046       4821
Elapsed: 00:00:00.00

xxxx> @ &r/viewsess 'storage'
NAME                                                                     STATISTIC#        VALUE          SID
---------------------------------------------------------------------- ------------ ------------ ------------
cell physical IO bytes saved by storage index                                   274  15562743808         4821

--//15562743808/1024/1024/1024 = 14.49393463134765625
--//15562743808/1024/1024 = 14841.7890625
--//15562743808/8192 = 1899749块

--//竟然存储索引可以使用.我以为会失效.也许前面的部分数据是使用expdp导入的(我当时记忆5XG),可能发生行链接或者迁移的量很少.估计开始
--//实施也不规范,XXkey的字段都是NULL.我估计仅仅没有发生行迁移或者链接的存储单元1M的数据才有存储索引.(我的理解)
--//看看与cell相关的记数变化情况:

xxxx> @ &r/viewsess 'cell'
NAME                                                                     STATISTIC#        VALUE          SID
---------------------------------------------------------------------- ------------ ------------ ------------
cell writes to flash cache                                                       58            0         4821
cell overwrites in flash cache                                                   59            0         4821
cell partial writes in flash cache                                               60            0         4821
cell physical IO interconnect bytes                                              64  33219425400         4821
cell physical IO bytes saved during optimized file creation                     271            0         4821
cell physical IO bytes saved during optimized RMAN file restore                 272            0         4821
cell physical IO bytes eligible for predicate offload                           273 222633656320         4821
cell physical IO bytes saved by storage index                                   274  15562743808         4821
cell physical IO bytes sent directly to DB node to balance CPU                  275            0         4821
cell smart IO session cache lookups                                             276            0         4821
cell smart IO session cache hits                                                277            0         4821
cell smart IO session cache soft misses                                         278            0         4821
cell smart IO session cache hard misses                                         279            0         4821
cell smart IO session cache hwm                                                 280            0         4821
cell num smart IO sessions in rdbms block IO due to user                        281            0         4821
cell num smart IO sessions in rdbms block IO due to open fail                   282            0         4821
cell num smart IO sessions in rdbms block IO due to no cell mem                 283            0         4821
cell num smart IO sessions in rdbms block IO due to big payload                 284            0         4821
cell num smart IO sessions using passthru mode due to user                      285            0         4821
cell num smart IO sessions using passthru mode due to cellsrv                   286            0         4821
cell num smart IO sessions using passthru mode due to timezone                  287            0         4821
cell num smart file creation sessions using rdbms block IO mode                 288            0         4821
cell num block IOs due to a file instant restore in progress                    289            0         4821
cell physical IO interconnect bytes returned by smart scan                      290   6552450168         4821
cell num bytes in passthru during predicate offload                             291            0         4821
cell num bytes in block IO during predicate offload                             292            0         4821
cell num fast response sessions                                                 293            0         4821
cell num fast response sessions continuing to smart scan                        294            0         4821
cell num smartio automem buffer allocation attempts                             295            1         4821
cell num smartio automem buffer allocation failures                             296            0         4821
cell statistics spare1                                                          297            0         4821
cell statistics spare2                                                          298            0         4821
cell statistics spare3                                                          299            0         4821
cell statistics spare4                                                          300            0         4821
cell statistics spare5                                                          301            0         4821
cell statistics spare6                                                          302            0         4821
cell scans                                                                      421            1         4821
cell blocks processed by cache layer                                            422     25661755         4821
cell blocks processed by txn layer                                              423     25661095         4821
cell blocks processed by data layer                                             424     25282464         4821
cell blocks processed by index layer                                            425            0         4821
cell commit cache queries                                                       426            0         4821
cell transactions found in commit cache                                         427            0         4821
cell blocks helped by commit cache                                              428            0         4821
cell blocks helped by minscn optimization                                       429     25647939         4821
chained rows skipped by cell                                                    430      3467111         4821
chained rows processed by cell                                                  431      1116529         4821
chained rows rejected by cell                                                   432      3467111         4821
cell simulated physical IO bytes eligible for predicate offload                 433            0         4821
cell simulated physical IO bytes returned by predicate offload                  434            0         4821
cell CUs sent uncompressed                                                      435            0         4821
cell CUs sent compressed                                                        436            0         4821
cell CUs sent head piece                                                        437            0         4821
cell CUs processed for uncompressed                                             438            0         4821
cell CUs processed for compressed                                               439            0         4821
cell IO uncompressed bytes                                                      440 207119351808         4821
cell index scans                                                                457            0         4821
cell flash cache read hits                                                      646      3138149         4821

58 rows selected.

--//对于许多记数不是很熟悉,仅仅做一个记录.

--//附上viewsess.sql脚本:
set verify off
column name format a70
SELECT b.NAME, a.statistic#, a.VALUE,a.sid
  FROM v$mystat a, v$statname b
 WHERE lower(b.NAME) like lower('%&1%') AND a.statistic# = b.statistic# ;
 --and a.value>0;

[20180730]exadata与行链接.txt的更多相关文章

  1. Oracle 行迁移和行链接

    一.行迁移 1.1.行迁移概念 当一个行上的更新操作(原来的数据存在且没有减少)导致当前的数据不能在容纳在当前块,我们需要进行行迁移.一个行迁移意味着整行数据将会移动,仅仅保留的是一个转移地址.因此整 ...

  2. 参数化时按行读取txt文件,如何去掉换行符"\n"

    参数化按行读取txt,每行默认自带了回车换行操作,导致脚本报错,故而按行读取时,需要去掉默认的'\n' #coding=utf-8 from selenium import webdriver imp ...

  3. 模拟Oracle行迁移和行链接

    行链接消除方法创建大的block块------------------ 参考tom kyte的例子----------------------------------------------创建4k ...

  4. java指定编码的按行读写txt文件(几种读写方式的比较)

    转: java指定编码的按行读写txt文件(几种读写方式的比较) 2018年10月16日 20:40:02 Handoking 阅读数:976  版权声明:本文为博主原创文章,未经博主允许不得转载. ...

  5. [20191010]bash行计算器.txt

    [20191010]bash行计算器.txt --//写一个bash行计算器,为了避免冲突,函数命名为2个=,1个=感觉不是很好(心里上^_^).--//使用bc计算器,里面函数不能使用圆括号,使用中 ...

  6. C语言:按行读TXT文件

    //搂行读取TXT #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_L ...

  7. Python中将变量按行写入txt文本中

    案例一: 讲数组a 循环写入名称为2.txt的文档中 # -*-coding:utf8-*- import requests from lxml import etree a=[1,2,3,4,5,6 ...

  8. 按行读取TXT文件中的内容

    public Dictionary<int, string> GetDicFromLog() { try { StreamReader sr = new StreamReader(file ...

  9. java按行读取txt并按行写入

    IO流想必大家都很熟悉了,本次实现的需求是按行读取文件内容并且按行写入,代码如下: try { String encoding="utf-8"; //设定自己需要的字符编码集 Fi ...

随机推荐

  1. 【Promise】Promise实现请求超时处理(基本版)

    首先是没有加入请求超时的情况: var http = require('http'); var url = require('url'); function get(addr) { return ne ...

  2. C语言实现多态

    C语言实现多态 首先声明,大神就不要看了.小弟水平有限. C++多态是通过虚函数表实现的,类似于JAVA多态的实现方式.关于Java多态的实现方式可以看我之前写过的一篇不是很完善的文章.从JVM角度看 ...

  3. Spring Boot初识(4)- Spring Boot整合JWT

    一.本文介绍 上篇文章讲到Spring Boot整合Swagger的时候其实我就在思考关于接口安全的问题了,在这篇文章了我整合了JWT用来保证接口的安全性.我会先简单介绍一下JWT然后在上篇文章的基础 ...

  4. 认识Nginx,理解原理和功能

    前端工程师在理解Nginx之后,就能更好的与后端工程师沟通,为了能提高工作效率,这两天抽空读了<Nginx高性能Web服务器实战教程>. 一.Nginx Nginx是一款高性能的Web服务 ...

  5. 一直性hash解决扩容后的hash算法不用变

    转自: http://blog.codinglabs.org/articles/consistent-hashing.html 摘要 本文将会从实际应用场景出发,介绍一致性哈希算法(Consisten ...

  6. macOS 系统 .DS_Store 文件详解

    .DS_Store 文件 .DS_Store 是 Finder 用来存储这个文件夹的显示属性的:比如文件图标的摆放位置. 显示/隐藏 Mac 隐藏文件 显示:defaults write com.ap ...

  7. python中逻辑运算符“+”的特殊之处

    num = num + num 与 num += num 的区别(其他语言中这两种方式可以划等号,但是python中不可以): num = num + num: num = [100] def tes ...

  8. Shell 示例:利用 $RANDOM 产生随机整数

    代码如下: #!/bin/bash # $RANDOM 在每次调用的时候,返回一个不同的随机整数 # 指定的范围是: 0 - 32767 MAXCOUNT=10 count=1 echo echo & ...

  9. NLog 配置

    之前我介绍过如何使用log4net来记录日志,但最近喜欢上了另一个简单好用的日志框架NLog. 关于NLog和log4net的比较这里就不多讨论了,感兴趣的朋友可以参看.NET日志工具介绍和log4n ...

  10. ASP .NET MVC HtmlHelper扩展——简化“列表控件”的绑定

    在众多表单元素中,有一类<select>元素用于绑定一组预定义列表.传统的ASP.NET Web Form中,它对应着一组重要的控件类型,即ListControl,我们经常用到DropDo ...