背景

Redis Cluser采用虚拟槽分区，所有的键根据哈希函数映射到0~16383个整数槽内，计算公式：slot=CRC16（key）&16383。
redis的key如果是数字自增，例如group01, group02, group03是否会全部落在相邻的点槽点上，从而打到同一台redis机器上？

结论

java的hash算法，对group01, group02, group03这种得到的hash值是相邻的
redis用的是CRC16算法，对group01, group02, group03算出的hash值是不相邻的，所以算出的槽位不会相邻

参考

redis cluster怎么保证键的均匀分配（crc16算法）
CRC16校验–java方式实现
循环冗余检验 (CRC) 算法原理

java版本的CRC16

没有实际验证过，不能保证计算正确，仅供参考

public class RedisCRC16 {//crc16tab数组，便于进行“查表法”计算crc结果，提高效率, 直接拷贝过来，uint16_t数组用int表示没有问题private static  int[] crc16tab = {0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,0x9339,0x8318,0xb37b,0xa35a,0xd3bd,0xc39c,0xf3ff,0xe3de,0x2462,0x3443,0x0420,0x1401,0x64e6,0x74c7,0x44a4,0x5485,0xa56a,0xb54b,0x8528,0x9509,0xe5ee,0xf5cf,0xc5ac,0xd58d,0x3653,0x2672,0x1611,0x0630,0x76d7,0x66f6,0x5695,0x46b4,0xb75b,0xa77a,0x9719,0x8738,0xf7df,0xe7fe,0xd79d,0xc7bc,0x48c4,0x58e5,0x6886,0x78a7,0x0840,0x1861,0x2802,0x3823,0xc9cc,0xd9ed,0xe98e,0xf9af,0x8948,0x9969,0xa90a,0xb92b,0x5af5,0x4ad4,0x7ab7,0x6a96,0x1a71,0x0a50,0x3a33,0x2a12,0xdbfd,0xcbdc,0xfbbf,0xeb9e,0x9b79,0x8b58,0xbb3b,0xab1a,0x6ca6,0x7c87,0x4ce4,0x5cc5,0x2c22,0x3c03,0x0c60,0x1c41,0xedae,0xfd8f,0xcdec,0xddcd,0xad2a,0xbd0b,0x8d68,0x9d49,0x7e97,0x6eb6,0x5ed5,0x4ef4,0x3e13,0x2e32,0x1e51,0x0e70,0xff9f,0xefbe,0xdfdd,0xcffc,0xbf1b,0xaf3a,0x9f59,0x8f78,0x9188,0x81a9,0xb1ca,0xa1eb,0xd10c,0xc12d,0xf14e,0xe16f,0x1080,0x00a1,0x30c2,0x20e3,0x5004,0x4025,0x7046,0x6067,0x83b9,0x9398,0xa3fb,0xb3da,0xc33d,0xd31c,0xe37f,0xf35e,0x02b1,0x1290,0x22f3,0x32d2,0x4235,0x5214,0x6277,0x7256,0xb5ea,0xa5cb,0x95a8,0x8589,0xf56e,0xe54f,0xd52c,0xc50d,0x34e2,0x24c3,0x14a0,0x0481,0x7466,0x6447,0x5424,0x4405,0xa7db,0xb7fa,0x8799,0x97b8,0xe75f,0xf77e,0xc71d,0xd73c,0x26d3,0x36f2,0x0691,0x16b0,0x6657,0x7676,0x4615,0x5634,0xd94c,0xc96d,0xf90e,0xe92f,0x99c8,0x89e9,0xb98a,0xa9ab,0x5844,0x4865,0x7806,0x6827,0x18c0,0x08e1,0x3882,0x28a3,0xcb7d,0xdb5c,0xeb3f,0xfb1e,0x8bf9,0x9bd8,0xabbb,0xbb9a,0x4a75,0x5a54,0x6a37,0x7a16,0x0af1,0x1ad0,0x2ab3,0x3a92,0xfd2e,0xed0f,0xdd6c,0xcd4d,0xbdaa,0xad8b,0x9de8,0x8dc9,0x7c26,0x6c07,0x5c64,0x4c45,0x3ca2,0x2c83,0x1ce0,0x0cc1,0xef1f,0xff3e,0xcf5d,0xdf7c,0xaf9b,0xbfba,0x8fd9,0x9ff8,0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0};public static int crc16(String str) {return crc16(str, str.length());}//具体的crc16算法实现public static int crc16(String str, int len) {int counter;int crc = 0;for (counter = 0; counter < len; counter++) {crc = getUnsignedInt16(getUnsignedInt16((crc << 8)) ^ crc16tab[((crc >> 8) ^ str.charAt(counter))&0x00FF]);}return crc;}public static int getUnsignedInt16(int data) {// c语言的uint16_t的数值范围是0-65535return data & 0x0FFFF;}public static int keyHashSlot(String key) {return keyHashSlot(key, key.length());}// 计算给定键应该被分配到哪个槽public static int keyHashSlot(String key, int keylen) {int s, e; /* start-end indexes of { and } */for (s = 0; s < keylen; s++)if (key.charAt(s) == '{') break;/* No '{' ? Hash the whole key. This is the base case. *///0x3FFF转化成十进制就是16383if (s == keylen) return crc16(key,keylen) & 0x3FFF;/* '{' found? Check if we have the corresponding '}'. */for (e = s+1; e < keylen; e++)if (key.charAt(e) == '}') break;/* No '}' or nothing betweeen {} ? Hash the whole key. */if (e == keylen || e == s+1) return crc16(key,keylen) & 0x3FFF;/* If we are here there is both a { and a } on its right. Hash* what is in the middle between { and }. */return crc16(key.substring(s+1),e-s-1) & 0x3FFF;}// 这个CRC计算的结果和模拟redis计算的CRC结果一致，多了7倍循环效率会低一些，抄自https://blog.csdn.net/qq_39835384/article/details/97045693public static int CRC_XModem(byte[] bytes){int crc = 0x00;int polynomial = 0x1021;for (int index = 0 ; index< bytes.length; index++) {byte b = bytes[index];for (int i = 0; i < 8; i++) {boolean bit = ((b   >> (7-i) & 1) == 1);boolean c15 = ((crc >> 15    & 1) == 1);crc <<= 1;if (c15 ^ bit) crc ^= polynomial;}}crc &= 0xffff;return crc;}public static void main(String[] args) {System.out.println("group01".hashCode()); //输出293427392System.out.println("group02".hashCode()); //输出293427393System.out.println("group03".hashCode()); //输出293427394System.out.println("group04".hashCode()); //输出293427395System.out.println(crc16("group01")); //输出7544System.out.println(crc16("group02")); //输出11547System.out.println(crc16("group03")); //输出15674System.out.println(crc16("group04")); //输出19933System.out.println(keyHashSlot("group01")); //输出7544System.out.println(keyHashSlot("group02")); //输出11547System.out.println(keyHashSlot("group03")); //输出15674System.out.println(keyHashSlot("group04")); //输出3549System.out.println(keyHashSlot("{group04}00")); //输出3549System.out.println(keyHashSlot("{group04}10")); //输出3549System.out.println(CRC_XModem("group01".getBytes(StandardCharsets.UTF_8))); //hash输出7544，和模拟redis的crc16算出结果一致System.out.println(CRC_XModem("group02".getBytes(StandardCharsets.UTF_8))); //hash输出11547，和模拟redis的crc16算出结果一致System.out.println(CRC_XModem("group03".getBytes(StandardCharsets.UTF_8))); //hash输出15674，和模拟redis的crc16算出结果一致System.out.println(CRC_XModem("group04".getBytes(StandardCharsets.UTF_8))); //hash输出19933，和模拟redis的crc16算出结果一致}
}

java版CRC16计算redis的key槽点相关推荐

java程序RedisTempla往redis存key后在redis客户端获取不到key
原因可能是使用程序中的redis代码执行了更换数据库的操作,而不是使用默认的0号数据库遇到的情况如下: redis的RDB数据库有18条key,但使用keys和DBSIZE命令均无法查看到程序添加 ...
腾讯开放平台接口鉴权（计算签名）工具类 java版
腾讯开放平台接口鉴权(签名)工具类 java版用到了Hutool工具类 package top.seasmall.platform.core.config.nettyws.util;import ...
Java版CRC8和CRC16工具类
搞物联应用,通信时常用CRC校验.下面是Java版的CRC算法工具类,可直接使用. CRC8工具类 public class CRC8Util {static byte[] crc8_tab = {( ...
**Java有哪些悲观锁的实现_80% 人不知道的 Redis 分布式锁的正确实现方式（Java 版）...
点击上方"小哈学Java",选择"星标" 回复"资源",领取全网最火的Java核心知识总结来源:http://sina.lt/gfZU 前 ...
阿里云短信验证解决方案(java版)(redis存储)
阿里云短信验证解决方案(java版)(redis存储) 参考文章: (1)阿里云短信验证解决方案(java版)(redis存储) (2)https://www.cnblogs.com/Amos-Tur ...
Redis分布式锁的正确实现方式（Java版）
转自:https://wudashan.cn/2017/10/23/Redis-Distributed-Lock-Implement/ 前言分布式锁一般有三种实现方式:1. 数据库乐观锁:2. 基于 ...
用 Redis 实现分布式锁（Java 版）
用 Redis 实现分布式锁(Java 版) 核心代码完整代码分布式锁是一种解决分布式临界资源并发读写的一种技术.本文详细介绍了在 Java 中使用 Redis 实现分布式锁的方法.为了方便, ...
数值分析北航第八题第三次计算实习任务（附百度云源码java版）
先上干货 ,包含word报告与源码. 链接:https://pan.baidu.com/s/1piPSQIqsBcLH_pHAYog5tw 提取码:55jo 稍加说明,这是java版的源码以及上交作业 ...
C语言实验——圆柱体计算(C语言版 java版）
Problem Description 已知圆柱体的底面半径r和高h,计算圆柱体底面周长和面积.圆柱体侧面积以及圆柱体体积.其中圆周率定义为3.1415926. Input 输入数据有一行,包括2个正 ...

java版CRC16计算redis的key槽点

背景

结论

参考

java版本的CRC16

java版CRC16计算redis的key槽点相关推荐

最新文章

热门文章