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Adds consistent hashing with bound loads sharding algorithm
Signed-off-by: Akram Ben Aissi <akram.benaissi@gmail.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,288 @@ | ||
| // 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 | ||
| package consistent | ||
|
|
||
| import ( | ||
| "encoding/binary" | ||
| "errors" | ||
| "fmt" | ||
| "math" | ||
| "sync" | ||
| "sync/atomic" | ||
|
|
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| "github.com/google/btree" | ||
|
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| blake2b "github.com/minio/blake2b-simd" | ||
| ) | ||
|
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| var ErrNoHosts = errors.New("no hosts added") | ||
|
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| type Host struct { | ||
| Name string | ||
| Load int64 | ||
| } | ||
|
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| type Consistent struct { | ||
| servers map[uint64]string | ||
| clients *btree.BTree | ||
| loadMap map[string]*Host | ||
| totalLoad int64 | ||
| replicationFactor int | ||
|
|
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| sync.RWMutex | ||
| } | ||
|
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| type item struct { | ||
| value uint64 | ||
| } | ||
|
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| func (i item) Less(than btree.Item) bool { | ||
| return i.value < than.(item).value | ||
| } | ||
|
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| func New() *Consistent { | ||
| return &Consistent{ | ||
| servers: map[uint64]string{}, | ||
| clients: btree.New(2), | ||
| loadMap: map[string]*Host{}, | ||
| replicationFactor: 1000, | ||
| } | ||
| } | ||
|
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| func NewWithReplicationFactor(replicationFactor int) *Consistent { | ||
| return &Consistent{ | ||
| servers: map[uint64]string{}, | ||
| clients: btree.New(2), | ||
| loadMap: map[string]*Host{}, | ||
| replicationFactor: replicationFactor, | ||
| } | ||
| } | ||
| func (c *Consistent) Add(server string) { | ||
| c.Lock() | ||
| defer c.Unlock() | ||
|
|
||
| if _, ok := c.loadMap[server]; ok { | ||
| return | ||
| } | ||
|
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| c.loadMap[server] = &Host{Name: server, Load: 0} | ||
| for i := 0; i < c.replicationFactor; i++ { | ||
| h := c.hash(fmt.Sprintf("%s%d", server, i)) | ||
| c.servers[h] = server | ||
| c.clients.ReplaceOrInsert(item{h}) | ||
| } | ||
| } | ||
|
|
||
| // Get returns the server that owns the given client. | ||
| // As described in https://en.wikipedia.org/wiki/Consistent_hashing | ||
| // It returns ErrNoHosts if the ring has no servers in it. | ||
| func (c *Consistent) Get(client string) (string, error) { | ||
| c.RLock() | ||
| defer c.RUnlock() | ||
|
|
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| if c.clients.Len() == 0 { | ||
| return "", ErrNoHosts | ||
| } | ||
|
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| h := c.hash(client) | ||
| var foundItem btree.Item | ||
| c.clients.AscendGreaterOrEqual(item{h}, func(i btree.Item) bool { | ||
| foundItem = i | ||
| return false // stop the iteration | ||
| }) | ||
|
|
||
| if foundItem == nil { | ||
| // If no host found, wrap around to the first one. | ||
| foundItem = c.clients.Min() | ||
| } | ||
|
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| host := c.servers[foundItem.(item).value] | ||
|
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| return host, nil | ||
| } | ||
|
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| // GetLeast returns the least loaded host that can serve the key. | ||
| // It uses Consistent Hashing With Bounded loads. | ||
| // https://research.googleblog.com/2017/04/consistent-hashing-with-bounded-loads.html | ||
| // It returns ErrNoHosts if the ring has no hosts in it. | ||
| func (c *Consistent) GetLeast(client string) (string, error) { | ||
| c.RLock() | ||
| defer c.RUnlock() | ||
|
|
||
| if c.clients.Len() == 0 { | ||
| return "", ErrNoHosts | ||
| } | ||
|
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| h := c.hash(client) | ||
| idx := c.search(h) | ||
|
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| i := idx | ||
| for { | ||
| x := item{uint64(i)} | ||
| key := c.clients.Get(x) | ||
| if key != nil { | ||
| host := c.servers[key.(*item).value] | ||
| if c.loadOK(host) { | ||
| return host, nil | ||
| } | ||
| i++ | ||
| if i >= c.clients.Len() { | ||
| i = 0 | ||
| } | ||
| } else { | ||
| return client, nil | ||
| } | ||
| } | ||
| } | ||
|
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| func (c *Consistent) search(key uint64) int { | ||
| idx := 0 | ||
| found := false | ||
|
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| c.clients.Ascend(func(i btree.Item) bool { | ||
| if i.(item).value >= key { | ||
| found = true | ||
| return false // stop the iteration | ||
| } | ||
| idx++ | ||
| return true | ||
| }) | ||
|
|
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| if !found { | ||
| idx = 0 | ||
| } | ||
|
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| return idx | ||
| } | ||
|
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| // Sets the load of `server` to the given `load` | ||
| func (c *Consistent) UpdateLoad(server string, load int64) { | ||
| c.Lock() | ||
| defer c.Unlock() | ||
|
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| if _, ok := c.loadMap[server]; !ok { | ||
| return | ||
| } | ||
| c.totalLoad -= c.loadMap[server].Load | ||
| c.loadMap[server].Load = load | ||
| c.totalLoad += load | ||
| } | ||
|
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| // Increments the load of host by 1 | ||
| // | ||
| // should only be used with if you obtained a host with GetLeast | ||
| func (c *Consistent) Inc(server string) { | ||
| c.Lock() | ||
| defer c.Unlock() | ||
|
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| if _, ok := c.loadMap[server]; !ok { | ||
| return | ||
| } | ||
| atomic.AddInt64(&c.loadMap[server].Load, 1) | ||
| atomic.AddInt64(&c.totalLoad, 1) | ||
| } | ||
|
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| // Decrements the load of host by 1 | ||
| // | ||
| // should only be used with if you obtained a host with GetLeast | ||
| func (c *Consistent) Done(server string) { | ||
| c.Lock() | ||
| defer c.Unlock() | ||
|
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| if _, ok := c.loadMap[server]; !ok { | ||
| return | ||
| } | ||
| atomic.AddInt64(&c.loadMap[server].Load, -1) | ||
| atomic.AddInt64(&c.totalLoad, -1) | ||
| } | ||
|
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| // Deletes host from the ring | ||
| func (c *Consistent) Remove(server string) bool { | ||
| c.Lock() | ||
| defer c.Unlock() | ||
|
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| for i := 0; i < c.replicationFactor; i++ { | ||
| h := c.hash(fmt.Sprintf("%s%d", server, i)) | ||
| delete(c.servers, h) | ||
| c.delSlice(h) | ||
| } | ||
| delete(c.loadMap, server) | ||
| return true | ||
| } | ||
|
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| // Return the list of servers in the ring | ||
| func (c *Consistent) Servers() (servers []string) { | ||
| c.RLock() | ||
| defer c.RUnlock() | ||
| for k := range c.loadMap { | ||
| servers = append(servers, k) | ||
| } | ||
| return servers | ||
| } | ||
|
|
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| // Returns the loads of all the hosts | ||
| func (c *Consistent) GetLoads() map[string]int64 { | ||
| loads := map[string]int64{} | ||
|
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| for k, v := range c.loadMap { | ||
| loads[k] = v.Load | ||
| } | ||
| return loads | ||
| } | ||
|
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| // 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) | ||
| } | ||
|
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| func (c *Consistent) loadOK(server string) bool { | ||
| // a safety check if someone performed c.Done more than needed | ||
| if c.totalLoad < 0 { | ||
| c.totalLoad = 0 | ||
| } | ||
|
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| var avgLoadPerNode float64 | ||
| avgLoadPerNode = float64((c.totalLoad + 1) / int64(len(c.loadMap))) | ||
| if avgLoadPerNode == 0 { | ||
| avgLoadPerNode = 1 | ||
| } | ||
| avgLoadPerNode = math.Ceil(avgLoadPerNode * 1.25) | ||
|
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| bserver, ok := c.loadMap[server] | ||
| if !ok { | ||
| panic(fmt.Sprintf("given host(%s) not in loadsMap", bserver.Name)) | ||
| } | ||
|
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| if float64(bserver.Load)+1 <= avgLoadPerNode { | ||
| return true | ||
| } | ||
|
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| return false | ||
| } | ||
|
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| func (c *Consistent) delSlice(val uint64) { | ||
| c.clients.Delete(item{val}) | ||
| } | ||
|
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| func (c *Consistent) hash(key string) uint64 { | ||
| out := blake2b.Sum512([]byte(key)) | ||
| return binary.LittleEndian.Uint64(out[:]) | ||
| } |
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