touchdown - 博客园

MySQL索引原理和慢查询优化

摘要： MySQL用的是B+ tree索引。数据是存储在磁盘上的，所以如果是索引是基于二叉树的话，这样涉及到很多次的磁盘I/O，I/O次数取决于树的高度，大大降低了查询的速度。使用B+树这种多路搜索树结构，可以三次I/O实现百万级数据的查询。建立索引的原则：最左前缀匹配原则，非常重要的原则，mysql会阅读全文

posted @ 2016-12-14 11:58 touchdown 阅读(279) 评论(0) 推荐(0)

浏览器中输入google.com，点击回车后会发生什么？

摘要：解析URL 浏览器能够通过URL知道下面信息： Protocol：http ->使用http协议 index： "/"，请求主页 1. 浏览器从缓存中查询域名 2. 如果缓存中没有，进行DNS查询，分为本地DNS服务器和ISP缓存服务器 3. 浏览器得到目标IP地址和相应的port，然后建立sock 阅读全文

posted @ 2016-12-13 13:18 touchdown 阅读(139) 评论(0) 推荐(0)

abstract class and interface

摘要： Interface separates what a Class does and how does it work. List interface lets different type of List to implement its own method. interface has more 阅读全文

posted @ 2016-12-11 09:10 touchdown 阅读(98) 评论(0) 推荐(0)

final, static

摘要： static class is used to when you don't need to instantiate the class. Like Math class, instantiating it is unnecessary. Final class prevents extension 阅读全文

posted @ 2016-12-11 02:00 touchdown 阅读(160) 评论(0) 推荐(0)

为什么重写equals方法必须重写hashCode？

摘要：如果两个对象调用equals返回相等，那么这两个对象调用hashCode方法必须返回相同的整数。如果不重写hashCode，会违反该原则。这个原则主要针对的是映射操作（map接口）。注意： 1. String重写了Object的equals，现在比较的是两个String所包含的char seque 阅读全文

posted @ 2016-12-04 02:10 touchdown 阅读(112) 评论(0) 推荐(0)

一致性哈希(Consistent Hashing)

摘要：传统来讲，数据的存储位置是通过hash(object)%N来计算的，这样造成的问题是如果新的机器添加进来或是某台机器down掉了，通过这种算法计算出来的存储位置会和以前的不同，造成了大量数据的迁移，如果有新的机器添加进来也会造成同样的问题，所以容错性和扩展性都不好。一致性哈希算法的主要目的是尽量减少阅读全文

posted @ 2016-11-12 04:56 touchdown 阅读(131) 评论(0) 推荐(0)

Java generics

摘要： Prior to Java 5, there are a lot of casting in collections, since in collection you add objects and cast the object you get back from collection. Prov 阅读全文

posted @ 2016-02-19 01:39 touchdown 阅读(166) 评论(0) 推荐(0)

If application data needs to be sent to IP address xx.xx.xx.xx, how does it work in underneath network?

摘要： This is to illustrate the communication between two separate machines which don't have a direct physical connection. Application data is generated and 阅读全文

posted @ 2016-02-14 01:18 touchdown 阅读(178) 评论(0) 推荐(0)

Projects_Tweets Analysis

摘要： This is a course project of real time big data analysis. My idea is to use tweets to extract trending topics and analyze political popularity using Ha 阅读全文

posted @ 2016-02-04 22:32 touchdown 阅读(167) 评论(0) 推荐(0)

Recommendation Systems

摘要： The key data that drives most recommendation systems is user behavior data. There are two main types of user behavior data: implicit user feedback dat 阅读全文

posted @ 2016-02-03 04:02 touchdown 阅读(207) 评论(0) 推荐(0)