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转载 SELECT AS in WHERE

First, you cannot use ALIAS on the WHERE clause. You should be using the column,SELECT SUBSTRING(rating, INSTR(rating,',') +1, +2) AS val FROM users WHERE SUBSTRING(rating, INSTR(rating,','

2015-06-30 11:58:30 411

转载 Finding Duplicate Records Using GROUP BY in SQL Server

There are various times when we need to find duplicate records in SQL Server. It is possible to find duplicates using DISTINCT, ROW NUMBER as well as the GROUP BY approach.Duplicate records ca

2015-06-29 19:03:37 346

转载 How to Extend/Reduce LVM’s (Logical Volume Management) in Linux – Part II

Previously we have seen how to create a flexible disk storage using LVM. Here, we are going to see how to extend volume group, extend and reduce a logical volume. Here we can reduce or extend the part

2015-05-24 10:38:32 456

转载 Setup Flexible Disk Storage with Logical Volume Management (LVM) in Linux – PART 1

Logical Volume Management (LVM) makes it easier to manage disk space. If a file system needs more space, it can be added to its logical volumes from the free spaces in its volume group and the file

2015-05-24 10:37:26 284

转载 Architecture of a Highly Scalable NIO-Based Server

ContentsThreading ArchitectureThe Reactor PatternComponent ArchitectureAcceptorDispatcherDispatcher-Level EventHandlerApplication-Level EventHandlerConclusionResourcesIf you are asked to w

2015-05-21 15:37:09 239

转载 Java NIO Tutorial

Read more http://tutorials.jenkov.com/java-nio/index.html

2015-05-21 14:18:21 200

转载动态规划的逆向思维法

动态规划是一种思维方法，没有统一的、具体的模式。动态规划可以从多方面去考察，不同的方面对动态规划有不同的表述。我们不打算强加一种统一的表述，而是从多个角度对动态规划的思维方法进行讨论，希望大家在思维具体问题时，也能够从多个角度展开，这样收获会更大。逆向思维法是指从问题目标状态出发倒推回初始状态或边界状态的思维方法。如果原问题可以分解成几个本质相同、规模较小的问题，很自然就会联想到从逆向

2015-05-05 18:36:16 1289

转载最大堆的插入/删除/调整/排序操作

堆有最大堆和最小堆之分，最大堆就是每个节点的值都>=其左右孩子（如果有的话）值的完全二叉树。最小堆便是每个节点的值都设有n个元素的序列{k1,k2,...,kn},当且仅当满足下列关系时,称之为堆。堆的三种基本操作(以下以最大堆为例)： ⑴最大堆的插入由于需要维持完全二叉树的形态，需要先将要插入的结点x放在最底层的最右边，插入后满足完全二叉树

2015-05-04 18:26:40 224

转载 Understanding Java Garbage Collection

What are the benefits of knowing how garbage collection (GC) works in Java? Satisfying the intellectual curiosity as a software engineer would be a valid cause, but also, understanding how GC works

2015-05-04 10:05:27 215

转载 The Principles of Java Application Performance Tuning

This is the fifth article in the series of "Become a Java GC Expert". In the first issue Understanding Java Garbage Collection we have learned about the processes for different GC algorithms, about

2015-04-30 17:42:22 203

转载 Design Patterns Uncovered: The Facade Pattern

This article will focus on the Facade pattern. So far in our design patterns we've already looked at the Observer and Adapterpatterns. Facade has some similarities with the Adapter, so it's a logica

2015-04-29 16:33:36 301

转载 Design Patterns Uncovered: The Adapter Pattern

Continuing our series of articles, taking each design pattern one by one, we move onto the Adapter pattern. This pattern is used a lot in Eclipse, allowing plug-ins to be loosely coupled, yet still be

2015-04-29 16:27:34 386

转载 Design Patterns Uncovered: The Proxy Pattern

Today's pattern is the Proxy pattern, another simple but effective pattern that helps with controlling use and access of resources. Proxy in the Real World A Proxy can also be defined as a sur

2015-04-29 15:59:16 388

转载 MySQL Engines - MyISAM vs Innodb

MySQL supports several different types of Table Engines also known as "Table Types". A database can have its tables being a mix of different table engine types or all of the same type. Here is more in

2015-04-27 18:38:02 305

转载 Java Memory Model

Table of ContentsThe Internal Java Memory ModelHardware Memory ArchitectureBridging The Gap Between The Java Memory Model And The Hardware Memory ArchitectureVisibility of Shared ObjectsRa

2015-04-21 19:25:06 223

转载 Have you ever tried installing Apache 2.4.4 in Linux.?

Just for sometime I was away from my blogging, but recently had to touch the pages for self signed certs in WebLogic Server on one of my friends request, hoping to get the blogging on the track from

2015-04-20 10:48:34 230

转载 Connection Establishment in TCP

Identifying a TCP ConnectionTCP connection:A TCP connection is a logical connection between 2 communicating entities.Packets from each TCP connection are uniquely identified

2015-04-13 23:44:34 539

转载 TCP: terminating a connection

Terminating a TCP connectionClosing a TCP connection is a much easiest than establishing a TCP connection (it is usually easier to destroy than to build....)The process is very much like ord

2015-04-13 23:41:30 481

转载 Best Practices for Speeding Up Your Web Site

The Exceptional Performance team has identified a number of best practices for making web pages fast. The list includes 35 best practices divided into 7 categories.Filter by category:

2015-04-11 13:19:31 372

转载 Speeding Up The Linux Kernel With Transparent Hugepage Support

Last month we reported on the 200 line Linux kernel patch that does wonders for improving the desktop responsiveness of the system. There was certainly much interest (over 100,000 views to both of o

2015-04-09 11:11:11 415

转载 Gain 30% Linux Disk Performance with noatime, nodiratime, and relatime

This is post #8 in my December 2013 series about Linux Virtual Machine Performance Tuning. For more, please see the tag “Linux VM Performance Tuning.”According to Red Hat’s Enterprise Linux 6

2015-04-08 18:04:35 248

转载 OOM relation to vm.swappiness=0 in new kernel

I have recently been involved in diagnosing the reasons behind OOM invocation that would kill the MySQL server process. Of course these servers were primarily running MySQL. As such the MySQL server p

2015-04-08 17:37:27 480

转载 Installing NRPE (Nagios Client) on CentOS 5

What is Nagios?from nagios.org/about Get proactive. Save time, money, and your sanity. Nagios is the industry standard in enterprise-class monitoring for good reason. It allows you to gain insight

2015-04-02 18:11:34 367

转载 Top 15 System and Performance Monitoring Tools for Linux

System monitoring is the primary responsibility of every System Administrator. I think every system admin must know few command line and few automatic system monitoring tools. In this article, I am pr

2015-04-02 15:27:56 350

转载 How To Install and Configure NRPE on CentOS, Redhat

NRPE is called as ‘Nagios Remote Plugin Executere‘. NRPE allows nagios server to remotely execute plugins on other Linux/Unix machines. NRPE is also available with some windows addons to monitor win

2015-04-02 14:58:57 185

转载 How to Install Nagios 4.0.8 (Monitoring Server) on CentOS, Red Hat & Fedora

Nagios is the most popular, open source, powerful monitoring system. It enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes. Nagio

2015-04-02 14:55:34 217

转载 IFS – Internal Field Separator

It seems like an esoteric concept, but it’s actually very useful.If your input file is “1 apple steve@example.com”, then your script could say:while read qty product customerdo echo "${custom

2015-04-01 15:22:20 326

转载 String.intern in Java 6, 7 and 8 – string pooling

This article will describe how String.intern method was implemented in Java 6 and what changes were made in it in Java 7 and Java 8.First of all I want to thank Yannis Bres for inspiring me to

2015-03-31 14:06:46 225

转载 Memory consumption of popular Java data types

This article will give you an overview of some popular Java data types memory consumption. This article follows An overview of memory saving techniques in Java article earlier published in this blog

2015-03-31 13:14:56 201

转载 Trove library: using primitive collections for performance

19 July 2014: article text cleanup, added a chapter on JDK to Trove migration.16 July 2012: original version.This article would describe Trove library, which contains a set of primitive coll

2015-03-31 11:59:33 297

转载 An overview of memory saving techniques in Java

An overview of memory saving techniques in Javaby Mikhail VorontsovThis article will give you the general advices on memory consumption optimization in Java.Memory usage optimization is

2015-03-31 11:54:04 226

转载 Tiered Compilation

Gadzooks, time flies! Been too long since I blogged… no time for something deep so here’s another quicky brain dump.Azul Systems has been running HotSpot with a Tiered Compilation system since 200

2015-03-31 10:56:31 483

转载 Making operations on volatile fields atomic

OverviewThe expected behaviour for volatile fields is that they should behave in a multi-threaded application the same as they do in a single threaded application. They are not forbidden to behav

2015-03-25 00:01:48 1289

转载 Apache Hadoop YARN: Avoiding 6 Time-Consuming "Gotchas"

Understanding some key differences between MR1 and MR2/YARN will make your migration much easier.Here at Cloudera, we recently finished a push to get Cloudera Enterprise 5 (containing CDH 5.0.0

2015-03-23 13:22:12 375

转载最短路径之Dijkstra算法详细讲解

最短路径之Dijkstra算法详细讲解 2009-01-12 23:08:48| 分类： 3S|举报|字号订阅１最短路径算法在日常生活中，我们如果需要常常往返A地区和B地区之间，我们最希望知道的可能是从A地区到B地区间的众多路径中，那一条路径的路途最短。最短路径问题是图论研究中的一个经典算法问题，旨在寻找图（由结点和路径组成的）中两结点之间的最短路径。算

2015-03-21 19:16:22 268

转载一个链表问题：复制带随机指针的链表

一个链表问题：复制带随机指针的链表题目:有一个链表L,其每个节点有2个指针，一个指针next指向链表的下个节点，另一个random随机指向链表中的任一个节点，可能是自己或者为空，写一个程序，要求复制这个链表的结构并分析其复杂性解决方法一：O(n)的复杂度,扫面两边即可。

2015-03-21 17:46:02 223

转载动态规划：从新手到专家

March 26, 2013作者：Hawstein出处：http://hawstein.com/posts/dp-novice-to-advanced.html声明：本文采用以下协议进行授权：自由转载-非商用-非衍生-保持署名|Creative Commons BY-NC-ND 3.0 ，转载请注明作者及出处。前言本文翻译自TopCoder上的一篇文章：

2015-03-21 13:58:48 217

转载 Hadoop Performance Tuning Best Practices

I have been working on Hadoop in production for a while. Here are some of the performance tuning tips I learned from work. Many of my tasks had performance improved over 50% in general. Those guide li

2015-03-20 15:29:01 258

转载 Hadoop Interview Questions

Hadoop is a complex framework. Some interview questions can be really simple like “How do you debug a performance issue or a long running job?” but difficult to answer on the spot if you are not prep

2015-03-20 14:34:39 279

转载 Determine YARN and MapReduce Memory Configuration Settings

This section describes how to configure YARN and MapReduce memory allocation settings based on the node hardware specifications.YARN takes into account all of the available compute resources on each

2015-03-20 13:54:46 227