一致性哈希算法
常用负载均衡算法：轮询、按权重、一致性哈希
分布式系统负载均衡的首选算法(
consisten Hashing)负载场景：
接入机后端带N台服务器，接入机收到请求将请求均匀的分发到每台服务器上。
每台服务器需要处理N/1的请求
如何解决用户数据缓存的问题？
我们如果现在的
Server1上有Cleint 1的缓存数据，但是第二次请求被发送到了Server2上面，而Server2上并没有Cleint1的数据。这个时候就需要使用远程的缓存服务器redis来解决这个问题，而不是在服务器1里面取数据。如果是大流量，高并发场景呢？
那我们可以使用
redis服务器做集群部署，让用户的数据均匀的分发到集群的每一台服务器上。总结：一个良好的分布式哈希方案应该具有良好的单调性，即服务的结点的增减不会导致大量哈希的重新定位。
算法描述
- 一致性哈希算法将整个哈希值空间理解成一个环，取值范围是0~2^32-1，也就是4GB的空间
- 将所有的服务器进行哈希，都落在一致性哈希环上
- 进行负载时，先将哈希输入值得到一致性哈希环上的一个哈希值，然后沿着顺时针，遇到的第一台服务器就是最终的负载到的服务器
算法实现
主要是一致性哈希算法的代码实现
md5算法
我们所需要的md5算法的核心代码实现
md5.h
/* typedef a 32 bit type */
typedef unsigned long int UINT4;
/* Data structure for MD5 (Message Digest) computation */
typedef struct {
UINT4 i[2]; /* number of _bits_ handled mod 2^64 */
UINT4 buf[4]; /* scratch buffer */
unsigned char in[64]; /* input buffer */
unsigned char digest[16]; /* actual digest after MD5Final call */
} MD5_CTX;
void MD5Init(MD5_CTX* mdContext);
void MD5Update(MD5_CTX* mdContext, unsigned char* inBuf, unsigned int inLen);
void MD5Final(MD5_CTX* mdContext);
static void Transform(UINT4* buf, UINT4* in);
// 指定一个文件的路径path，根据文件内容计算出一个md5加密串
char* MD5_file(const char* path, int md5_len=32);
// 从原始的字符串，得到加密后的md5串
char* MD5(const char* buf, int md5_len = 32);
// 把32位的md5串，处理成unsigned int返回
unsigned int getMD5(const char* buf);
md5.cc
#include "md5.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* forward declaration */
static void Transform();
static unsigned char PADDING[64] = {
0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};
/* F, G and H are basic MD5 functions: selection, majority, parity */
#define F(x, y, z) (((x) & (y)) | ((~x) & (z)))
#define G(x, y, z) (((x) & (z)) | ((y) & (~z)))
#define H(x, y, z) ((x) ^ (y) ^ (z))
#define I(x, y, z) ((y) ^ ((x) | (~z)))
/* ROTATE_LEFT rotates x left n bits */
#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4 */
/* Rotation is separate from addition to prevent recomputation */
#define FF(a, b, c, d, x, s, ac) \
{(a) += F ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
#define GG(a, b, c, d, x, s, ac) \
{(a) += G ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
#define HH(a, b, c, d, x, s, ac) \
{(a) += H ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
#define II(a, b, c, d, x, s, ac) \
{(a) += I ((b), (c), (d)) + (x) + (UINT4)(ac); \
(a) = ROTATE_LEFT ((a), (s)); \
(a) += (b); \
}
void MD5Init(MD5_CTX* mdContext)
{
mdContext->i[0] = mdContext->i[1] = (UINT4)0;
/* Load magic initialization constants.
*/
mdContext->buf[0] = (UINT4)0x67452301;
mdContext->buf[1] = (UINT4)0xefcdab89;
mdContext->buf[2] = (UINT4)0x98badcfe;
mdContext->buf[3] = (UINT4)0x10325476;
}
void MD5Update(MD5_CTX* mdContext, unsigned char* inBuf, unsigned int inLen)
{
UINT4 in[16];
int mdi;
unsigned int i, ii;
/* compute number of bytes mod 64 */
mdi = (int)((mdContext->i[0] >> 3) & 0x3F);
/* update number of bits */
if ((mdContext->i[0] + ((UINT4)inLen << 3)) < mdContext->i[0])
mdContext->i[1]++;
mdContext->i[0] += ((UINT4)inLen << 3);
mdContext->i[1] += ((UINT4)inLen >> 29);
while (inLen--) {
/* add new character to buffer, increment mdi */
mdContext->in[mdi++] = *inBuf++;
/* transform if necessary */
if (mdi == 0x40) {
for (i = 0, ii = 0; i < 16; i++, ii += 4)
in[i] = (((UINT4)mdContext->in[ii + 3]) << 24) |
(((UINT4)mdContext->in[ii + 2]) << 16) |
(((UINT4)mdContext->in[ii + 1]) << 8) |
((UINT4)mdContext->in[ii]);
Transform(mdContext->buf, in);
mdi = 0;
}
}
}
void MD5Final(MD5_CTX* mdContext)
{
UINT4 in[16];
int mdi;
unsigned int i, ii;
unsigned int padLen;
/* save number of bits */
in[14] = mdContext->i[0];
in[15] = mdContext->i[1];
/* compute number of bytes mod 64 */
mdi = (int)((mdContext->i[0] >> 3) & 0x3F);
/* pad out to 56 mod 64 */
padLen = (mdi < 56) ? (56 - mdi) : (120 - mdi);
MD5Update(mdContext, PADDING, padLen);
/* append length in bits and transform */
for (i = 0, ii = 0; i < 14; i++, ii += 4)
in[i] = (((UINT4)mdContext->in[ii + 3]) << 24) |
(((UINT4)mdContext->in[ii + 2]) << 16) |
(((UINT4)mdContext->in[ii + 1]) << 8) |
((UINT4)mdContext->in[ii]);
Transform(mdContext->buf, in);
/* store buffer in digest */
for (i = 0, ii = 0; i < 4; i++, ii += 4) {
mdContext->digest[ii] = (unsigned char)(mdContext->buf[i] & 0xFF);
mdContext->digest[ii + 1] =
(unsigned char)((mdContext->buf[i] >> 8) & 0xFF);
mdContext->digest[ii + 2] =
(unsigned char)((mdContext->buf[i] >> 16) & 0xFF);
mdContext->digest[ii + 3] =
(unsigned char)((mdContext->buf[i] >> 24) & 0xFF);
}
}
/* Basic MD5 step. Transform buf based on in.
*/
static void Transform(UINT4* buf, UINT4* in)
{
UINT4 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
/* Round 1 */
#define S11 7
#define S12 12
#define S13 17
#define S14 22
FF(a, b, c, d, in[0], S11, 3614090360); /* 1 */
FF(d, a, b, c, in[1], S12, 3905402710); /* 2 */
FF(c, d, a, b, in[2], S13, 606105819); /* 3 */
FF(b, c, d, a, in[3], S14, 3250441966); /* 4 */
FF(a, b, c, d, in[4], S11, 4118548399); /* 5 */
FF(d, a, b, c, in[5], S12, 1200080426); /* 6 */
FF(c, d, a, b, in[6], S13, 2821735955); /* 7 */
FF(b, c, d, a, in[7], S14, 4249261313); /* 8 */
FF(a, b, c, d, in[8], S11, 1770035416); /* 9 */
FF(d, a, b, c, in[9], S12, 2336552879); /* 10 */
FF(c, d, a, b, in[10], S13, 4294925233); /* 11 */
FF(b, c, d, a, in[11], S14, 2304563134); /* 12 */
FF(a, b, c, d, in[12], S11, 1804603682); /* 13 */
FF(d, a, b, c, in[13], S12, 4254626195); /* 14 */
FF(c, d, a, b, in[14], S13, 2792965006); /* 15 */
FF(b, c, d, a, in[15], S14, 1236535329); /* 16 */
/* Round 2 */
#define S21 5
#define S22 9
#define S23 14
#define S24 20
GG(a, b, c, d, in[1], S21, 4129170786); /* 17 */
GG(d, a, b, c, in[6], S22, 3225465664); /* 18 */
GG(c, d, a, b, in[11], S23, 643717713); /* 19 */
GG(b, c, d, a, in[0], S24, 3921069994); /* 20 */
GG(a, b, c, d, in[5], S21, 3593408605); /* 21 */
GG(d, a, b, c, in[10], S22, 38016083); /* 22 */
GG(c, d, a, b, in[15], S23, 3634488961); /* 23 */
GG(b, c, d, a, in[4], S24, 3889429448); /* 24 */
GG(a, b, c, d, in[9], S21, 568446438); /* 25 */
GG(d, a, b, c, in[14], S22, 3275163606); /* 26 */
GG(c, d, a, b, in[3], S23, 4107603335); /* 27 */
GG(b, c, d, a, in[8], S24, 1163531501); /* 28 */
GG(a, b, c, d, in[13], S21, 2850285829); /* 29 */
GG(d, a, b, c, in[2], S22, 4243563512); /* 30 */
GG(c, d, a, b, in[7], S23, 1735328473); /* 31 */
GG(b, c, d, a, in[12], S24, 2368359562); /* 32 */
/* Round 3 */
#define S31 4
#define S32 11
#define S33 16
#define S34 23
HH(a, b, c, d, in[5], S31, 4294588738); /* 33 */
HH(d, a, b, c, in[8], S32, 2272392833); /* 34 */
HH(c, d, a, b, in[11], S33, 1839030562); /* 35 */
HH(b, c, d, a, in[14], S34, 4259657740); /* 36 */
HH(a, b, c, d, in[1], S31, 2763975236); /* 37 */
HH(d, a, b, c, in[4], S32, 1272893353); /* 38 */
HH(c, d, a, b, in[7], S33, 4139469664); /* 39 */
HH(b, c, d, a, in[10], S34, 3200236656); /* 40 */
HH(a, b, c, d, in[13], S31, 681279174); /* 41 */
HH(d, a, b, c, in[0], S32, 3936430074); /* 42 */
HH(c, d, a, b, in[3], S33, 3572445317); /* 43 */
HH(b, c, d, a, in[6], S34, 76029189); /* 44 */
HH(a, b, c, d, in[9], S31, 3654602809); /* 45 */
HH(d, a, b, c, in[12], S32, 3873151461); /* 46 */
HH(c, d, a, b, in[15], S33, 530742520); /* 47 */
HH(b, c, d, a, in[2], S34, 3299628645); /* 48 */
/* Round 4 */
#define S41 6
#define S42 10
#define S43 15
#define S44 21
II(a, b, c, d, in[0], S41, 4096336452); /* 49 */
II(d, a, b, c, in[7], S42, 1126891415); /* 50 */
II(c, d, a, b, in[14], S43, 2878612391); /* 51 */
II(b, c, d, a, in[5], S44, 4237533241); /* 52 */
II(a, b, c, d, in[12], S41, 1700485571); /* 53 */
II(d, a, b, c, in[3], S42, 2399980690); /* 54 */
II(c, d, a, b, in[10], S43, 4293915773); /* 55 */
II(b, c, d, a, in[1], S44, 2240044497); /* 56 */
II(a, b, c, d, in[8], S41, 1873313359); /* 57 */
II(d, a, b, c, in[15], S42, 4264355552); /* 58 */
II(c, d, a, b, in[6], S43, 2734768916); /* 59 */
II(b, c, d, a, in[13], S44, 1309151649); /* 60 */
II(a, b, c, d, in[4], S41, 4149444226); /* 61 */
II(d, a, b, c, in[11], S42, 3174756917); /* 62 */
II(c, d, a, b, in[2], S43, 718787259); /* 63 */
II(b, c, d, a, in[9], S44, 3951481745); /* 64 */
buf[0] += a;
buf[1] += b;
buf[2] += c;
buf[3] += d;
}
char* MD5_file(const char* path, int md5_len)
{
FILE* fp = fopen(path, "rb");
MD5_CTX mdContext;
int bytes;
unsigned char data[1024];
char* file_md5;
int i;
if (fp == NULL) {
fprintf(stderr, "fopen %s failed\n", path);
return NULL;
}
MD5Init(&mdContext);
while ((bytes = fread(data, 1, 1024, fp)) != 0)
{
MD5Update(&mdContext, data, bytes);
}
MD5Final(&mdContext);
file_md5 = (char*)malloc((md5_len + 1) * sizeof(char));
if (file_md5 == NULL)
{
fprintf(stderr, "malloc failed.\n");
return NULL;
}
memset(file_md5, 0, (md5_len + 1));
if (md5_len == 16)
{
for (i = 4; i < 12; i++)
{
sprintf(&file_md5[(i - 4) * 2], "%02x", mdContext.digest[i]);
}
}
else if (md5_len == 32)
{
for (i = 0; i < 16; i++)
{
sprintf(&file_md5[i * 2], "%02x", mdContext.digest[i]);
}
}
else
{
fclose(fp);
free(file_md5);
return NULL;
}
fclose(fp);
return file_md5;
}
char* MD5(const char* buf, int md5_len)
{
MD5_CTX mdContext;
int bytes;
unsigned char data[1024];
char* file_md5;
int i;
MD5Init(&mdContext);
MD5Update(&mdContext, (unsigned char*)buf, strlen(buf));
MD5Final(&mdContext);
file_md5 = (char*)malloc((md5_len + 1) * sizeof(char));
if (file_md5 == NULL)
{
fprintf(stderr, "malloc failed.\n");
return NULL;
}
memset(file_md5, 0, (md5_len + 1));
if (md5_len == 16)
{
for (i = 4; i < 12; i++)
{
sprintf(&file_md5[(i - 4) * 2], "%02x", mdContext.digest[i]);
}
}
else if (md5_len == 32)
{
for (i = 0; i < 16; i++)
{
sprintf(&file_md5[i * 2], "%02x", mdContext.digest[i]);
}
}
else
{
free(file_md5);
return NULL;
}
return file_md5;
}
unsigned int getMD5(const char* buf)
{
char* b = MD5(buf);
unsigned int hash = 0;
// 共32位的加密串 8个字符 4组
// 5f93f983524def3dca464469d2cf9f3e
for (int i = 0; i < 8; i++)
{
hash += ((int)(b[i * 4 + 3] & 0xFF) << 24)
| ((int)(b[i * 4 + 2] & 0xFF) << 16)
| ((int)(b[i * 4 + 1] & 0xFF) << 8)
| ((int)(b[i * 4 + 0] & 0xFF));
}
return hash;
}
生成物理结点
// 物理节点
class PhscialHost
{
public:
PhscialHost(string ip, int vnumber)
: ip_(ip)
{
for (int i = 0; i < vnumber; i++)
{
// 虚拟节点需要一个ip，还需要记录它属于哪个物理节点
virtualHosts_.emplace_back(
ip + "#" + ::to_string(i),
this
);
}
}
string getIP() const
{
return ip_;
}
const list<VirtualHost>& getVirtualHosts() const
{
return virtualHosts_;
}
private:
string ip_; // 物理机器的ip地址
list<VirtualHost> virtualHosts_; // 存储虚拟节点列表
};
虚拟结点
class VirtualHost
{
public:
VirtualHost(string ip, PhscialHost* p)
: ip_(ip)
, phscialHost_(p)
{
md5_ = ::getMD5(ip_.c_str());
}
bool operator<(const VirtualHost& host) const
{
return md5_ < host.md5_;
}
bool operator==(const VirtualHost& host) const
{
return ip_ == host.ip_;
}
uint getMD5() const
{
return md5_;
}
const PhscialHost* getPhscialHost() const
{
return phscialHost_;
}
private:
string ip_; // 虚拟节点的ip信息
uint md5_; // 虚拟节点在一致性哈希环上的位置
PhscialHost* phscialHost_; // 虚拟节点隶属的物理节点
};
一致性哈希算法实现
// 一致性哈希算法代码实现
class ConsistentHash
{
public:
// 在一致性哈希环上添加物理主机的虚拟节点
void addHost(PhscialHost& host)
{
// 获取物理主机所有的虚拟节点列表
auto list = host.getVirtualHosts();
for (auto host : list)
{
hashCircle_.insert(host);
}
}
// 在一致性哈希环上删除物理主机的虚拟节点
void delHost(PhscialHost& host)
{
// 获取物理主机所有的虚拟节点列表
auto list = host.getVirtualHosts();
for (auto host : list)
{
auto it = hashCircle_.find(host);
if (it != hashCircle_.end())
{
// 在一致性哈希环上删除所有物理主机对应的虚拟节点
hashCircle_.erase(it);
}
}
}
// 返回负载的真实物理主机的ip信息
string getHost(string clientip) const
{
uint md5 = getMD5(clientip.c_str());
for (auto vhost : hashCircle_)
{
if (vhost.getMD5() > md5)
{
return vhost.getPhscialHost()->getIP();
}
}
// 映射从0开始遇见的第一个虚拟节点
return hashCircle_.begin()->getPhscialHost()->getIP();
}
private:
set<VirtualHost> hashCircle_; // 一致性哈希环
};
输出
