11 Hash tables    Many applications require a dynamic set that supports only the dictionary operations INSERT, SEARCH, and DELETE. For example, a compiler that translates a programming language maintains a symbol table, in which the keys of elements…

哈希表 红黑树实现的符号表可以保证对数级别的性能,但我们可以做得更好.哈希表实现的符号表提供了新的数据访问方式,插入和搜索操作可以在常数时间内完成(不支持和顺序有关的操作).所以,在很多情况下的简单符号表,用哈希表实现是最好的选择. hash functions 如果键是小整数,那么我们可以直接使用数组来实现符号表,把键当做数组索引,于是键 i 对应的值放在数组位置 i 上.哈希(散列)是这个简单方法的拓展,可以处理类型更复杂的键.通过数学计算把键转为数组索引,我们就可以用数组来查询(refer…

Reference: Compuer science Introduction: This computer science video describes the fundamental principles of the hash table data structure which allows for very fast insertion and retrieval of data. It covers commonly used hash algorithms for numeric…

/** * Copyright 2010 Tim Down. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LI…

13.4 横向扩展带来性能提升 很多NoSQL系统都是基于键值模型的,因此其查询条件也基本上是基于键值的查询,基本不会有对整个数据进行查询的时候.由于基本上所有的查询操作都是基本键值形式的,因此分片通常也基于数据的键来做:键的一些属性会决定这个键值对存储在哪台机器上.下面我们将会对hash分片和范围分片两种分片方式进行描述. 3.4.2 通过协调器进行数据分片 由于CouchDB专注于单机性能,没有提供类似的横向扩展方案,于是出现了两个项目:Lounge 和 BigCouch,他们通过提供一个p…

HashMap 中hash table 定位算法: int hash = hash(key.hashCode()); int i = indexFor(hash, table.length); 其中indexFor和hash源码如下: /** * Applies a supplemental hash function to a given hashCode, which * defends against poor quality hash functions. This is critica…

Overview The u32 filter allows you to match on any bit field within a packet, so it is in some ways the most powerful filter provided by the Linux traffic control engine. It is also the most complex, and by far the hardest to use. To explain it I wil…

uthash 是C的比较优秀的开源代码,它实现了常见的hash操作函数,例如查找.插入.删除等.该套开源代码采用宏的方式实现hash函数的相关功能,支持C语言的任意数据结构最为key值,甚至可以采用多个值作为key,无论是自定义的struct还是基本数据类型,需要注意的是不同类型的key其操作接口方式略有不通. 使用uthash代码时只需要包含头文件"uthash.h"即可.由于该代码采用宏的方式实现,所有的实现代码都在uthash.h文件中,因此只需要在自己的代码中包含该头文件即可.…

源码: #ifndef _LINUX_HLIST_H #define _LINUX_HLIST_H /* * Double linked lists with a single pointer list head. * Mostly useful for hash tables where the two pointer list head is * too wasteful. * You lose the ability to access the tail in O(1). */ struc…

Hash function From Wikipedia, the free encyclopedia   A hash function that maps names to integers from 0 to 15. There is a collision between keys "John Smith" and "Sandra Dee". A hash function is any function that maps data of arbitrar…