架构师训练营第 0 期第 5 周作业

package main
import (
	"encoding/base64"
	"fmt"
	"log"
	"math/rand"
	"strconv"
	"github.com/carbocation/runningvariance"
	"stathat.com/c/consistent"
)
func main() {
	// 一致性哈希
	c := consistent.New()
	// 虚拟节点数
	c.NumberOfReplicas = 100
	// 10 个服务器节点
	numberOfServers := 10
	for i := 0; i < numberOfServers; i++ {
		c.Add("Server" + strconv.Itoa(i))
	}
	// 100 万 KV 数据
	pairs := map[string]int{}
	numberOfPairs := 1000000
	g := make([]byte, 12)
	for i := 0; i < numberOfPairs; i++ {
		_, err := rand.Read(g)
		if err != nil {
			log.Fatal(err)
		}
		s := base64.StdEncoding.EncodeToString(g)
		r, err := c.Get(s)
		if err != nil {
			log.Fatal(err)
		}
		pairs[r] += 1
	}
	// 统计信息
	r := runningvariance.NewRunningStat()
	for k, v := range pairs {
		fmt.Printf("%s: %d\n", k, v)
		r.Push(float64(v))
	}
	// 平均值
	mean := r.Mean()
	// 方差
	variance := r.Variance()
	// 标准差
	stdev := r.StandardDeviation()
	fmt.Printf("Mean: %f, Variance: %f, StdDev: %f\n", mean, variance, stdev)
}
// Output
// Server6: 107081
// Server9: 93514
// Server8: 83825
// Server3: 110271
// Server5: 116223
// Server7: 108069
// Server2: 108724
// Server1: 84023
// Server4: 110884
// Server0: 77386
// Mean: 100000.000000, Variance: 194317163.333333, StdDev: 13939.769128

// Copyright (C) 2012 Numerotron Inc.
// Use of this source code is governed by an MIT-style license
// that can be found in the LICENSE file.
// Package consistent provides a consistent hashing function.
//
// Consistent hashing is often used to distribute requests to a changing set of servers.  For example,
// say you have some cache servers cacheA, cacheB, and cacheC.  You want to decide which cache server
// to use to look up information on a user.
//
// You could use a typical hash table and hash the user id
// to one of cacheA, cacheB, or cacheC.  But with a typical hash table, if you add or remove a server,
// almost all keys will get remapped to different results, which basically could bring your service
// to a grinding halt while the caches get rebuilt.
//
// With a consistent hash, adding or removing a server drastically reduces the number of keys that
// get remapped.
//
// Read more about consistent hashing on wikipedia:  http://en.wikipedia.org/wiki/Consistent_hashing
//
package consistent // import "stathat.com/c/consistent"
import (
	"errors"
	"hash/crc32"
	"hash/fnv"
	"sort"
	"strconv"
	"sync"
)
type uints []uint32
// Len returns the length of the uints array.
func (x uints) Len() int { return len(x) }
// Less returns true if element i is less than element j.
func (x uints) Less(i, j int) bool { return x[i] < x[j] }
// Swap exchanges elements i and j.
func (x uints) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
// ErrEmptyCircle is the error returned when trying to get an element when nothing has been added to hash.
var ErrEmptyCircle = errors.New("empty circle")
// Consistent holds the information about the members of the consistent hash circle.
type Consistent struct {
	circle           map[uint32]string
	members          map[string]bool
	sortedHashes     uints
	NumberOfReplicas int
	count            int64
	scratch          [64]byte
	UseFnv           bool
	sync.RWMutex
}
// New creates a new Consistent object with a default setting of 20 replicas for each entry.
//
// To change the number of replicas, set NumberOfReplicas before adding entries.
func New() *Consistent {
	c := new(Consistent)
	c.NumberOfReplicas = 20
	c.circle = make(map[uint32]string)
	c.members = make(map[string]bool)
	return c
}
// eltKey generates a string key for an element with an index.
func (c *Consistent) eltKey(elt string, idx int) string {
	// return elt + "|" + strconv.Itoa(idx)
	return strconv.Itoa(idx) + elt
}
// Add inserts a string element in the consistent hash.
func (c *Consistent) Add(elt string) {
	c.Lock()
	defer c.Unlock()
	c.add(elt)
}
// need c.Lock() before calling
func (c *Consistent) add(elt string) {
	for i := 0; i < c.NumberOfReplicas; i++ {
		c.circle[c.hashKey(c.eltKey(elt, i))] = elt
	}
	c.members[elt] = true
	c.updateSortedHashes()
	c.count++
}
// Remove removes an element from the hash.
func (c *Consistent) Remove(elt string) {
	c.Lock()
	defer c.Unlock()
	c.remove(elt)
}
// need c.Lock() before calling
func (c *Consistent) remove(elt string) {
	for i := 0; i < c.NumberOfReplicas; i++ {
		delete(c.circle, c.hashKey(c.eltKey(elt, i)))
	}
	delete(c.members, elt)
	c.updateSortedHashes()
	c.count--
}
// Set sets all the elements in the hash.  If there are existing elements not
// present in elts, they will be removed.
func (c *Consistent) Set(elts []string) {
	c.Lock()
	defer c.Unlock()
	for k := range c.members {
		found := false
		for _, v := range elts {
			if k == v {
				found = true
				break
			}
		}
		if !found {
			c.remove(k)
		}
	}
	for _, v := range elts {
		_, exists := c.members[v]
		if exists {
			continue
		}
		c.add(v)
	}
}
func (c *Consistent) Members() []string {
	c.RLock()
	defer c.RUnlock()
	var m []string
	for k := range c.members {
		m = append(m, k)
	}
	return m
}
// Get returns an element close to where name hashes to in the circle.
func (c *Consistent) Get(name string) (string, error) {
	c.RLock()
	defer c.RUnlock()
	if len(c.circle) == 0 {
		return "", ErrEmptyCircle
	}
	key := c.hashKey(name)
	i := c.search(key)
	return c.circle[c.sortedHashes[i]], nil
}
func (c *Consistent) search(key uint32) (i int) {
	f := func(x int) bool {
		return c.sortedHashes[x] > key
	}
	i = sort.Search(len(c.sortedHashes), f)
	if i >= len(c.sortedHashes) {
		i = 0
	}
	return
}
// GetTwo returns the two closest distinct elements to the name input in the circle.
func (c *Consistent) GetTwo(name string) (string, string, error) {
	c.RLock()
	defer c.RUnlock()
	if len(c.circle) == 0 {
		return "", "", ErrEmptyCircle
	}
	key := c.hashKey(name)
	i := c.search(key)
	a := c.circle[c.sortedHashes[i]]
	if c.count == 1 {
		return a, "", nil
	}
	start := i
	var b string
	for i = start + 1; i != start; i++ {
		if i >= len(c.sortedHashes) {
			i = 0
		}
		b = c.circle[c.sortedHashes[i]]
		if b != a {
			break
		}
	}
	return a, b, nil
}
// GetN returns the N closest distinct elements to the name input in the circle.
func (c *Consistent) GetN(name string, n int) ([]string, error) {
	c.RLock()
	defer c.RUnlock()
	if len(c.circle) == 0 {
		return nil, ErrEmptyCircle
	}
	if c.count < int64(n) {
		n = int(c.count)
	}
	var (
		key   = c.hashKey(name)
		i     = c.search(key)
		start = i
		res   = make([]string, 0, n)
		elem  = c.circle[c.sortedHashes[i]]
	)
	res = append(res, elem)
	if len(res) == n {
		return res, nil
	}
	for i = start + 1; i != start; i++ {
		if i >= len(c.sortedHashes) {
			i = 0
		}
		elem = c.circle[c.sortedHashes[i]]
		if !sliceContainsMember(res, elem) {
			res = append(res, elem)
		}
		if len(res) == n {
			break
		}
	}
	return res, nil
}
func (c *Consistent) hashKey(key string) uint32 {
	if c.UseFnv {
		return c.hashKeyFnv(key)
	}
	return c.hashKeyCRC32(key)
}
func (c *Consistent) hashKeyCRC32(key string) uint32 {
	if len(key) < 64 {
		var scratch [64]byte
		copy(scratch[:], key)
		return crc32.ChecksumIEEE(scratch[:len(key)])
	}
	return crc32.ChecksumIEEE([]byte(key))
}
func (c *Consistent) hashKeyFnv(key string) uint32 {
	h := fnv.New32a()
	h.Write([]byte(key))
	return h.Sum32()
}
func (c *Consistent) updateSortedHashes() {
	hashes := c.sortedHashes[:0]
	//reallocate if we're holding on to too much (1/4th)
	if cap(c.sortedHashes)/(c.NumberOfReplicas*4) > len(c.circle) {
		hashes = nil
	}
	for k := range c.circle {
		hashes = append(hashes, k)
	}
	sort.Sort(hashes)
	c.sortedHashes = hashes
}
func sliceContainsMember(set []string, member string) bool {
	for _, m := range set {
		if m == member {
			return true
		}
	}
	return false
}

/*
runningvariance computes accurate running mean, variance, and standard deviation
It is based on code by John D Cook: http://www.johndcook.com/blog/standard_deviation/
*/
package runningvariance
import (
	"math"
)
type RunningStat struct {
	N    uint
	NewM float64
	OldM float64
	NewS float64
	OldS float64
}
func NewRunningStat() *RunningStat {
	return &RunningStat{}
}
func (r *RunningStat) Push(x float64) {
	r.N++
	// See Knuth TAOCP vol 2, 3rd edition, page 232
	if r.N == 1 {
		r.OldM = x
		r.NewM = x
		r.OldS = 0.0
	} else {
		r.NewM = r.OldM + (x-r.OldM)/float64(r.N)
		r.NewS = r.OldS + (x-r.OldM)*(x-r.NewM)
		// set up for next iteration
		r.OldM = r.NewM
		r.OldS = r.NewS
	}
}
func (r *RunningStat) NumDataValues() uint {
	return r.N
}
func (r *RunningStat) Mean() float64 {
	return r.NewM
}
func (r *RunningStat) Variance() float64 {
	if r.N > 1 {
		return r.NewS / (float64(r.N) - 1)
	}
	return 0.0
}
func (r *RunningStat) StandardDeviation() float64 {
	return math.Sqrt(r.Variance())
}