1.一般来说in比exists更有利(更容易变成join). 2.尽量避免union,使用union all代替,避免sort. 3,绝对不能在没有on条件下使用join(除非有特殊目的). 4.outer join的时候注意on和where.…

参考链接 Technote (troubleshooting) Problem(Abstract) Error [IBM][CLI Driver][DB2/6000] SQL0437W Performance for this complex querymay be sub-optimal.Reason Code "1". SQLSTATE=01602EXPENG-E-TYP1, The operation pack. is invalid for data type ,binary.…

1.减少查询对象的数据页(db block)数量. 尽量避免使用 * 用准确的列明减少不必要的一些资源浪费.   2.查看是否使用了index. 索引是SQL性能调优的重要手段,下面几个是有索引不能使用的情况. (1)在索引列中不进行加工. (2)不诱导索引列的数据类型转换. (3)比较null的时候使用 is null. (4)尽量避免使用非等号. (5)like计算的时候避免使用 “ %a ” .   3.用index代替sort.   4.hint是最后的手段. 为什么不建议使用hint,…

I've written multiple articles here at Javalobby on the Hibernate O/R mapping tool, and they are usually met with a large degree of popularity. Hibernate isn't just a popular kid on the block, however; it is actually a very powerful, consistent, and…

转自:https://iwringer.wordpress.com/2012/05/18/how-to-scale-complex-event-processing-cep-systems/ What is CEP? Complex event processing (CEP) systems query events on the fly without storing them. For an introduction and definition of CEP, please refer…

Don't fetch any data that you don't need,or don't fetch any columns that you don't need. Because retrieving more data or more columns, which can increase network,I/O,memory and CPU overhead for the server. For example, if you need several columns you…

refer: http://sqlblog.com/blogs/paul_white/archive/2012/04/28/query-optimizer-deep-dive-part-1.aspx    SQL是一种结构化查询语言规范,它从逻辑是哪个描述了用户需要的结果,而SQL服务器将这个逻辑需求描述转成能执行的物理执行计划,从而把结果返回给用户.将逻辑需求转换成一个更有效的物理执行计划的过程,就是优化的过程. 执行SQL的过程: Input Tree We start by looking…

Solr In Action 笔记(3) 之 SolrCloud基础 在Solr中,一个索引的实例称之为Core,而在SolrCloud中,一个索引的实例称之为Shard:Shard 又分为leader和replica. 1. SolrCloud的特质 作为分布式搜索引擎的SolrCloud具有以下几个特质: 可扩展性 所谓的可扩展性就是指可以通过扩大集群的规模来实现性能的提升.有两种方式来实现可扩展性,一种是纵向扩展,即加快CPU速度,增加RAM,提升磁盘I/O性能等,另一种是横向扩展,就是分…

摘要 : 本章节介绍NetExt常用的命令. 并且对SOS进行一些对比. NetExt的帮助 要想玩好NetExt, 入门就得看帮助. 看NetExt的帮助可以调用!whelp 命令. 这样hi列举出NetExt所支持的所有命令. 0:000> !netext.whelp netext version 2.0.0.5000 Feb 9 2015 License and usage can be seen here: !whelp license Check Latest version: !wu…

经过四天的努力终于将SqlSugar ORM 成功支持ORACLE数据库 优点: 1.高性能,达到原生最高水准,比SqlHelper性能要高,比Dapper快30% 比EF快50% 2.支持多种数据库 ,sql版本更新最快,其它会定期更新,可以在多种数据库用一种编程方式 3.支持.net Core 4.支持多库并行计算 5.带有实体生成函数和T4模版生成实体 6.无需任何配置 ,还你一个干净的model 2.功能介绍/Product function introduction 查询/Search…

This article is from blog of Amazon CTO Werner Vogels. -------------------- Today is a very exciting day as we release Amazon DynamoDB, a fast, highly reliable and cost-effective NoSQL database service designed for internet scale applications. Dynamo…

Reference to: http://www.c-sharpcorner.com/UploadFile/skumaar_mca/good-practices-to-write-the-stored-procedures-in-sql-server/ Use proper indentation for the statements in SQL Server. It will improve the readability. Write the proper comments between…

3.0最新API: http://www.cnblogs.com/sunkaixuan/p/5911334.html 1.前言/Preface SqlSugar从去年到现在已经一年了,版本从1.0升到了现在的2.8 ,这是一个稳定版本 ,有数家公司已经项目上线,在这里我将SqlSugar的功能重新整理成一篇新的贴子,希望大家喜欢. 公司团队项目.产品已经完全抛弃EF,SqlSugar定位不是ORM,而是为了方便的让你去写Sql. 媲美原生ADO.NET的性能.简洁的语法和支持Json .Dyna…

http://www.onjava.com/pub/a/onjava/2001/05/30/optimization.htmlComparing the performance of LinkedLists and ArrayLists (and Vectors) (Page last updated May 2001, Added 2001-06-18, Author Jack Shirazi, Publisher OnJava). Tips: ArrayList is faster than…

3.0最新API: http://www.cnblogs.com/sunkaixuan/p/5911334.html 1.前言/Preface SqlSugar从去年到现在已经一年了,版本从1.0升到了现在的2.8 ,这是一个稳定版本 ,有数家公司已经项目上线,在这里我将SqlSugar的功能重新整理成一篇新的贴子,希望大家喜欢. 公司团队项目.产品已经完全抛弃EF,SqlSugar定位不是ORM,而是为了方便的让你去写Sql. 媲美原生ADO.NET的性能.简洁的语法和支持Json .Dyna…

61. Evaluate the following SQL statements that are issued in the given order:CREATE TABLE emp(emp_no NUMBER(2) CONSTRAINT emp_emp_no_pk PRIMARY KEY,ename VARCHAR2(15),salary NUMBER(8,2),mgr_no NUMBER(2) CONSTRAINT emp_mgr_fk REFERENCES emp);ALTER TAB…

简介 官网:http://square.github.io/retrofit/ GitHub:https://github.com/square/retrofit/ compile 'com.squareup.retrofit2:retrofit:2.0.2' compile 'com.squareup.retrofit2:converter-gson:2.0.2' 在对Android 开发中,我们都是从原生的 HttpUrlConnection到经典的 Apache公司的HttpClient,…

* Be sure you really need to speed things up. Many of the ideas here are simple to try, but others will necessarily add some complexity to your application. So be sure your searching speed is indeed too slow and the slowness is indeed within Lucene.…

  package hcxAction; import hcxMode.Advertises; import hcxMode.Areas; import hcxMode.Saveresume; import hcxService.AdvertisesService; import hcxService.SaveresumeService; import java.io.File; import java.io.IOException; import java.util.List; import…

  今天介绍一款高颜值监控绘图工具Grafana,在使用Zabbix监控环境中,通常我们会结合Grafana进行图形展示.Grafana默认没有zabbix作为数据源,需要手动给zabbix安装一个插件,然后再添加进Grafana即可,非常简单.下面就介绍下Grafana的使用: Grafana的官网:http://docs.grafana.org/installation/rpm/ 1)Centos下的安装步骤 # wget https://s3-us-west-2.amazonaws.com…

1 compress & mr hive默认的execution engine是mr hive> set hive.execution.engine;hive.execution.engine=mr 所以针对mr的优化就是hive的优化,比如压缩和临时目录 mapred-site.xml <property> <name>mapreduce.map.output.compress</name> <value>true</value>…

On ROWNUM and Limiting Results Our technologist explains how ROWNUM works and how to make it work for you. By Tom Kyte  September/October 2006 This issue's Ask Tom column is a little different from the typical column. I receive many questions about h…

官方说法: work_mem (integer) Specifies the amount of memory to be used by internal sort operations and hash tables before writing to temporary disk files. The value defaults to four megabytes (4MB). Note that for a complex query, several sort or hash ope…

开发环境:VS2015 Xamarin Sqlite.NET ORM 不就相当于 Entiry Framework For Xamarin 吗? 相当于用 C# 开发安卓程序访问 Sqlite 可以使用 EF 了, 还支持CodeFirst ,再加上 linq,简直不要太帅啊. 亲测通过,转载原文,懒得翻译,备忘. 有兴趣的见官方:https://developer.xamarin.com/guides/android/application_fundamentals/data/part_3_u…

LAST UPDATE:     1 Dec 15, 2016 APPLIES TO:     1 2 3 4 Oracle Database - Enterprise Edition - Version 7.0.16.0 and later Oracle Database - Standard Edition - Version 7.0.16.0 and later Oracle Database - Personal Edition - Version 7.1.4.0 and later I…

几乎都是官方文档上的内容.     [ OFFSET offset { ROW | ROWS} ] [ FETCH { FIRST | NEXT }[ { rowcount | percent PERCENT } ]     { ROW| ROWS } { ONLY | WITH TIES } ]   row_limiting_clause   The row_limiting_clause allows you to limit therows returned by the query. Y…

简介 Retrofit 是一个Square开发的类型安全的REST安卓客户端请求库.这个库为网络认证.API请求以及用OkHttp发送网络请求提供了强大的框架.Retrofit库让从web api下载JSON 或者xml数据变的非常简单直接.一旦数据下载完成即将其解析成普通java类(POJO). Retrofit turns your HTTP API into a Java interface. Retrofit将你的HTTP API请求变为一个Java接口 public interface…

http://mysql.rjweb.org/bestof.html I have tagged many of the better forum threads. 'Better' is based on how good I thing the answer was. (<bias> I wrote many, but not all, of the better answers. </bias>) -- Rick James, MySQL Geek The Best of t…

Table of Contents The ProblemAlgorithmDigressionFirst, some examplesAlgorithm, Step 1 (WHERE "column = const")Algorithm, Step 2Algorithm, Step 2a (one range)Algorithm, Step 2b (GROUP BY)Algorithm, Step 2c (ORDER BY)Algorithm endLimitationsStop a…

快速向表中插入大量数据Oracle中append与Nologging 2017-05-05 / VIEWS: 304 来源于:http://blog.sina.com.cn/s/blog_61cd89f60102e7gi.html 当需要对一个非常大的表INSERT的时候,会消耗非常多的资源,因为update表的时候,oracle需要生成 redo log和undo log;此时最好的解决办法是用insert, 并且将表设置为nologging;当把表设为nologging后,并且使用的inse…