Add Redis Ring.

ring.go

@@ -0,0 +1,237 @@
+package redis
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"sync"
+	"time"
+
+	"github.com/golang/groupcache/consistenthash"
+)
+
+var (
+	errRingShardsDown = errors.New("redis: all ring shards are down")
+)
+
+// RingOptions are used to configure a ring client and should be
+// passed to NewRing.
+type RingOptions struct {
+	// A map of name => host:port addresses of ring shards.
+	Addrs map[string]string
+
+	// Following options are copied from Options struct.
+
+	DB       int64
+	Password string
+
+	DialTimeout  time.Duration
+	ReadTimeout  time.Duration
+	WriteTimeout time.Duration
+
+	PoolSize    int
+	PoolTimeout time.Duration
+	IdleTimeout time.Duration
+}
+
+func (opt *RingOptions) clientOptions() *Options {
+	return &Options{
+		DB:       opt.DB,
+		Password: opt.Password,
+
+		DialTimeout:  opt.DialTimeout,
+		ReadTimeout:  opt.ReadTimeout,
+		WriteTimeout: opt.WriteTimeout,
+
+		PoolSize:    opt.PoolSize,
+		PoolTimeout: opt.PoolTimeout,
+		IdleTimeout: opt.IdleTimeout,
+	}
+}
+
+type ringShard struct {
+	Client *Client
+	down   int
+}
+
+func (shard *ringShard) String() string {
+	var state string
+	if shard.IsUp() {
+		state = "up"
+	} else {
+		state = "down"
+	}
+	return fmt.Sprintf("%s is %s", shard.Client, state)
+}
+
+func (shard *ringShard) IsDown() bool {
+	const threshold = 5
+	return shard.down >= threshold
+}
+
+func (shard *ringShard) IsUp() bool {
+	return !shard.IsDown()
+}
+
+// Vote votes to set shard state and returns true if state was changed.
+func (shard *ringShard) Vote(up bool) bool {
+	if up {
+		changed := shard.IsDown()
+		shard.down = 0
+		return changed
+	}
+
+	if shard.IsDown() {
+		return false
+	}
+
+	shard.down++
+	return shard.IsDown()
+}
+
+// Ring is a Redis client that uses constistent hashing to distribute
+// keys across multiple Redis servers (shards).
+//
+// It monitors the state of each shard and removes dead shards from
+// the ring. When shard comes online it is added back to the ring. This
+// gives you maximum availability and partition tolerance, but no
+// consistency between different shards or even clients. Each client
+// uses shards that are available to the client and does not do any
+// coordination when shard state is changed.
+//
+// Ring should be used when you use multiple Redis servers for caching
+// and can tolerate losing data when one of the servers dies.
+// Otherwise you should use Redis Cluster.
+type Ring struct {
+	commandable
+
+	nreplicas int
+
+	mx     sync.RWMutex
+	hash   *consistenthash.Map
+	shards map[string]*ringShard
+
+	closed bool
+}
+
+func NewRing(opt *RingOptions) *Ring {
+	const nreplicas = 100
+	ring := &Ring{
+		nreplicas: nreplicas,
+		hash:      consistenthash.New(nreplicas, nil),
+		shards:    make(map[string]*ringShard),
+	}
+	ring.commandable.process = ring.process
+	for name, addr := range opt.Addrs {
+		clopt := opt.clientOptions()
+		clopt.Addr = addr
+		ring.addClient(name, NewClient(clopt))
+	}
+	go ring.heartbeat()
+	return ring
+}
+
+func (ring *Ring) addClient(name string, cl *Client) {
+	ring.mx.Lock()
+	ring.hash.Add(name)
+	ring.shards[name] = &ringShard{Client: cl}
+	ring.mx.Unlock()
+}
+
+func (ring *Ring) getClient(key string) (*Client, error) {
+	ring.mx.RLock()
+
+	if ring.closed {
+		return nil, errClosed
+	}
+
+	name := ring.hash.Get(key)
+	if name == "" {
+		ring.mx.RUnlock()
+		return nil, errRingShardsDown
+	}
+
+	if shard, ok := ring.shards[name]; ok {
+		ring.mx.RUnlock()
+		return shard.Client, nil
+	}
+
+	ring.mx.RUnlock()
+	return nil, errRingShardsDown
+}
+
+func (ring *Ring) process(cmd Cmder) {
+	cl, err := ring.getClient(hashKey(cmd.clusterKey()))
+	if err != nil {
+		cmd.setErr(err)
+		return
+	}
+	cl.baseClient.process(cmd)
+}
+
+// rebalance removes dead shards from the ring.
+func (ring *Ring) rebalance() {
+	defer ring.mx.Unlock()
+	ring.mx.Lock()
+
+	ring.hash = consistenthash.New(ring.nreplicas, nil)
+	for name, shard := range ring.shards {
+		if shard.IsUp() {
+			ring.hash.Add(name)
+		}
+	}
+}
+
+// heartbeat monitors state of each shard in the ring.
+func (ring *Ring) heartbeat() {
+	ticker := time.NewTicker(100 * time.Millisecond)
+	defer ticker.Stop()
+	for _ = range ticker.C {
+		var rebalance bool
+
+		ring.mx.RLock()
+
+		if ring.closed {
+			ring.mx.RUnlock()
+			break
+		}
+
+		for _, shard := range ring.shards {
+			err := shard.Client.Ping().Err()
+			if shard.Vote(err == nil) {
+				log.Printf("redis: ring shard state changed: %s", shard)
+				rebalance = true
+			}
+		}
+
+		ring.mx.RUnlock()
+
+		if rebalance {
+			ring.rebalance()
+		}
+	}
+}
+
+// Close closes the ring client, releasing any open resources.
+//
+// It is rare to Close a Client, as the Client is meant to be
+// long-lived and shared between many goroutines.
+func (ring *Ring) Close() (retErr error) {
+	defer ring.mx.Unlock()
+	ring.mx.Lock()
+
+	if ring.closed {
+		return nil
+	}
+	ring.closed = true
+
+	for _, shard := range ring.shards {
+		if err := shard.Client.Close(); err != nil {
+			retErr = err
+		}
+	}
+	ring.hash = nil
+	ring.shards = nil
+
+	return retErr
+}