/
consistent_hash.go
340 lines (290 loc) · 7.56 KB
/
consistent_hash.go
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// ------------------------------------------------------------
// Copyright (c) Microsoft Corporation and Dapr Contributors.
// Licensed under the MIT License.
// ------------------------------------------------------------
// Package placement is an implementation of Consistent Hashing and
// Consistent Hashing With Bounded Loads.
//
// https://en.wikipedia.org/wiki/Consistent_hashing
//
// https://research.googleblog.com/2017/04/consistent-hashing-with-bounded-loads.html
//
// https://github.com/lafikl/consistent/blob/master/consistent.go
//
package hashing
import (
"encoding/binary"
"fmt"
"math"
"sort"
"sync"
"sync/atomic"
blake2b "github.com/minio/blake2b-simd"
"github.com/pkg/errors"
)
var replicationFactor int
// ErrNoHosts is an error for no hosts.
var ErrNoHosts = errors.New("no hosts added")
// ConsistentHashTables is a table holding a map of consistent hashes with a given version.
type ConsistentHashTables struct {
Version string
Entries map[string]*Consistent
}
// Host represents a host of stateful entities with a given name, id, port and load.
type Host struct {
Name string
Port int64
Load int64
AppID string
}
// Consistent represents a data structure for consistent hashing.
type Consistent struct {
hosts map[uint64]string
sortedSet []uint64
loadMap map[string]*Host
totalLoad int64
sync.RWMutex
}
// NewPlacementTables returns new stateful placement tables with a given version.
func NewPlacementTables(version string, entries map[string]*Consistent) *ConsistentHashTables {
return &ConsistentHashTables{
Version: version,
Entries: entries,
}
}
// NewHost returns a new host.
func NewHost(name, id string, load int64, port int64) *Host {
return &Host{
Name: name,
Load: load,
Port: port,
AppID: id,
}
}
// NewConsistentHash returns a new consistent hash.
func NewConsistentHash() *Consistent {
return &Consistent{
hosts: map[uint64]string{},
sortedSet: []uint64{},
loadMap: map[string]*Host{},
}
}
// NewFromExisting creates a new consistent hash from existing values.
func NewFromExisting(hosts map[uint64]string, sortedSet []uint64, loadMap map[string]*Host) *Consistent {
return &Consistent{
hosts: hosts,
sortedSet: sortedSet,
loadMap: loadMap,
}
}
// GetInternals returns the internal data structure of the consistent hash.
func (c *Consistent) GetInternals() (map[uint64]string, []uint64, map[string]*Host, int64) {
c.RLock()
defer c.RUnlock()
return c.hosts, c.sortedSet, c.loadMap, c.totalLoad
}
// Add adds a host with port to the table.
func (c *Consistent) Add(host, id string, port int64) bool {
c.Lock()
defer c.Unlock()
if _, ok := c.loadMap[host]; ok {
return true
}
c.loadMap[host] = &Host{Name: host, AppID: id, Load: 0, Port: port}
for i := 0; i < replicationFactor; i++ {
h := c.hash(fmt.Sprintf("%s%d", host, i))
c.hosts[h] = host
c.sortedSet = append(c.sortedSet, h)
}
// sort hashes ascendingly
sort.Slice(c.sortedSet, func(i int, j int) bool {
return c.sortedSet[i] < c.sortedSet[j]
})
return false
}
// Get returns the host that owns `key`.
//
// As described in https://en.wikipedia.org/wiki/Consistent_hashing
//
// It returns ErrNoHosts if the ring has no hosts in it.
func (c *Consistent) Get(key string) (string, error) {
c.RLock()
defer c.RUnlock()
if len(c.hosts) == 0 {
return "", ErrNoHosts
}
h := c.hash(key)
idx := c.search(h)
return c.hosts[c.sortedSet[idx]], nil
}
// GetHost gets a host.
func (c *Consistent) GetHost(key string) (*Host, error) {
h, err := c.Get(key)
if err != nil {
return nil, err
}
return c.loadMap[h], nil
}
// GetLeast uses Consistent Hashing With Bounded loads
//
// https://research.googleblog.com/2017/04/consistent-hashing-with-bounded-loads.html
//
// to pick the least loaded host that can serve the key
//
// It returns ErrNoHosts if the ring has no hosts in it.
//
func (c *Consistent) GetLeast(key string) (string, error) {
c.RLock()
defer c.RUnlock()
if len(c.hosts) == 0 {
return "", ErrNoHosts
}
h := c.hash(key)
idx := c.search(h)
i := idx
for {
host := c.hosts[c.sortedSet[i]]
if c.loadOK(host) {
return host, nil
}
i++
if i >= len(c.hosts) {
i = 0
}
}
}
func (c *Consistent) search(key uint64) int {
idx := sort.Search(len(c.sortedSet), func(i int) bool {
return c.sortedSet[i] >= key
})
if idx >= len(c.sortedSet) {
idx = 0
}
return idx
}
// UpdateLoad sets the load of `host` to the given `load`.
func (c *Consistent) UpdateLoad(host string, load int64) {
c.Lock()
defer c.Unlock()
if _, ok := c.loadMap[host]; !ok {
return
}
c.totalLoad -= c.loadMap[host].Load
c.loadMap[host].Load = load
c.totalLoad += load
}
// Inc increments the load of host by 1
//
// should only be used with if you obtained a host with GetLeast.
func (c *Consistent) Inc(host string) {
c.Lock()
defer c.Unlock()
atomic.AddInt64(&c.loadMap[host].Load, 1)
atomic.AddInt64(&c.totalLoad, 1)
}
// Done decrements the load of host by 1
//
// should only be used with if you obtained a host with GetLeast.
func (c *Consistent) Done(host string) {
c.Lock()
defer c.Unlock()
if _, ok := c.loadMap[host]; !ok {
return
}
atomic.AddInt64(&c.loadMap[host].Load, -1)
atomic.AddInt64(&c.totalLoad, -1)
}
// Remove deletes host from the ring.
func (c *Consistent) Remove(host string) bool {
c.Lock()
defer c.Unlock()
for i := 0; i < replicationFactor; i++ {
h := c.hash(fmt.Sprintf("%s%d", host, i))
delete(c.hosts, h)
c.delSlice(h)
}
delete(c.loadMap, host)
return true
}
// Hosts return the list of hosts in the ring.
func (c *Consistent) Hosts() (hosts []string) {
c.RLock()
defer c.RUnlock()
for k := range c.loadMap {
hosts = append(hosts, k)
}
return hosts
}
// GetLoads returns the loads of all the hosts.
func (c *Consistent) GetLoads() map[string]int64 {
loads := map[string]int64{}
for k, v := range c.loadMap {
loads[k] = v.Load
}
return loads
}
// MaxLoad returns the maximum load of the single host
// which is:
// (total_load/number_of_hosts)*1.25
// total_load = is the total number of active requests served by hosts
// for more info:
// https://research.googleblog.com/2017/04/consistent-hashing-with-bounded-loads.html
func (c *Consistent) MaxLoad() int64 {
if c.totalLoad == 0 {
c.totalLoad = 1
}
var avgLoadPerNode float64
avgLoadPerNode = float64(c.totalLoad / int64(len(c.loadMap)))
if avgLoadPerNode == 0 {
avgLoadPerNode = 1
}
avgLoadPerNode = math.Ceil(avgLoadPerNode * 1.25)
return int64(avgLoadPerNode)
}
func (c *Consistent) loadOK(host string) bool {
// a safety check if someone performed c.Done more than needed
if c.totalLoad < 0 {
c.totalLoad = 0
}
var avgLoadPerNode float64
avgLoadPerNode = float64((c.totalLoad + 1) / int64(len(c.loadMap)))
if avgLoadPerNode == 0 {
avgLoadPerNode = 1
}
avgLoadPerNode = math.Ceil(avgLoadPerNode * 1.25)
bhost, ok := c.loadMap[host]
if !ok {
panic(fmt.Sprintf("given host(%s) not in loadsMap", bhost.Name))
}
if float64(bhost.Load)+1 <= avgLoadPerNode {
return true
}
return false
}
func (c *Consistent) delSlice(val uint64) {
idx := -1
l := 0
r := len(c.sortedSet) - 1
for l <= r {
m := (l + r) / 2
if c.sortedSet[m] == val {
idx = m
break
} else if c.sortedSet[m] < val {
l = m + 1
} else if c.sortedSet[m] > val {
r = m - 1
}
}
if idx != -1 {
c.sortedSet = append(c.sortedSet[:idx], c.sortedSet[idx+1:]...)
}
}
func (c *Consistent) hash(key string) uint64 {
out := blake2b.Sum512([]byte(key))
return binary.LittleEndian.Uint64(out[:])
}
// SetReplicationFactor sets the replication factor for actor placement on vnodes.
func SetReplicationFactor(factor int) {
replicationFactor = factor
}