Consistent hashing

CHANGELOG.md

@@ -18,6 +18,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 - [#5352](https://github.com/thanos-io/thanos/pull/5352) Cache: Add cache metrics to groupcache.
 - [#5391](https://github.com/thanos-io/thanos/pull/5391) Receive: Add relabeling support.
+- [#5408](https://github.com/thanos-io/thanos/pull/5391) Receive: Add support for consistent hashrings.
 
 ### Changed
 

cmd/thanos/receive.go

@@ -426,7 +426,7 @@ func setupHashring(g *run.Group,
 		ctx, cancel := context.WithCancel(context.Background())
 		g.Add(func() error {
 			level.Info(logger).Log("msg", "the hashring initialized with config watcher.")
-			return receive.HashringFromConfigWatcher(ctx, updates, cw)
+			return receive.HashringFromConfigWatcher(ctx, receive.HashringAlgorithm(conf.hashringsAlgorithm), updates, cw)
 		}, func(error) {
 			cancel()
 		})
@@ -437,7 +437,7 @@ func setupHashring(g *run.Group,
 		)
 		// The Hashrings config file content given initialize configuration from content.
 		if len(conf.hashringsFileContent) > 0 {
-			ring, err = receive.HashringFromConfig(conf.hashringsFileContent)
+			ring, err = receive.HashringFromConfig(receive.HashringAlgorithm(conf.hashringsAlgorithm), conf.hashringsFileContent)
 			if err != nil {
 				close(updates)
 				return errors.Wrap(err, "failed to validate hashring configuration file")
@@ -718,6 +718,7 @@ type receiveConfig struct {
 
 	hashringsFilePath    string
 	hashringsFileContent string
+	hashringsAlgorithm   string
 
 	refreshInterval   *model.Duration
 	endpoint          string
@@ -779,6 +780,8 @@ func (rc *receiveConfig) registerFlag(cmd extkingpin.FlagClause) {
 
 	cmd.Flag("receive.hashrings", "Alternative to 'receive.hashrings-file' flag (lower priority). Content of file that contains the hashring configuration.").PlaceHolder("<content>").StringVar(&rc.hashringsFileContent)
 
+	cmd.Flag("receive.hashrings-algorithm", "The algorithm used when distributing series in the hashrings.").Default(string(receive.AlgorithmHashmod)).EnumVar(&rc.hashringsAlgorithm, string(receive.AlgorithmHashmod), string(receive.AlgorithmConsistent))
+
 	rc.refreshInterval = extkingpin.ModelDuration(cmd.Flag("receive.hashrings-file-refresh-interval", "Refresh interval to re-read the hashring configuration file. (used as a fallback)").
 		Default("5m"))
 

docs/components/receive.md

@@ -126,6 +126,9 @@ Flags:
                                  Alternative to 'receive.hashrings-file' flag
                                  (lower priority). Content of file that contains
                                  the hashring configuration.
+      --receive.hashrings-algorithm=hashmod
+                                 The algorithm used when distributing series in
+                                 the hashrings.
       --receive.hashrings-file=<path>
                                  Path to file that contains the hashring
                                  configuration. A watcher is initialized to

pkg/receive/handler_test.go

@@ -324,7 +324,7 @@ func newTestHandlerHashring(appendables []*fakeAppendable, replicationFactor uin
 		cfg[0].Endpoints = append(cfg[0].Endpoints, h.options.Endpoint)
 		peers.cache[addr] = &fakeRemoteWriteGRPCServer{h: h}
 	}
-	hashring := newMultiHashring(cfg)
+	hashring := newMultiHashring(AlgorithmHashmod, cfg)
 	for _, h := range handlers {
 		h.Hashring(hashring)
 	}

pkg/receive/hashring.go

@@ -6,14 +6,31 @@ package receive
 import (
 	"context"
 	"fmt"
+	"sort"
+	"strconv"
 	"sync"
 
+	"github.com/cespare/xxhash"
+
 	"github.com/pkg/errors"
 	"github.com/thanos-io/thanos/pkg/store/labelpb"
 
 	"github.com/thanos-io/thanos/pkg/store/storepb/prompb"
 )
 
+// HashringAlgorithm is the algorithm used to distribute series in the ring.
+type HashringAlgorithm string
+
+const (
+	AlgorithmHashmod    HashringAlgorithm = "hashmod"
+	AlgorithmConsistent HashringAlgorithm = "consistent"
+
+	// SectionsPerNode is the number of sections in the ring assigned to each node
+	// when using consistent hashing. A higher number yields a better series distribution,
+	// but also comes with a higher memory cost.
+	SectionsPerNode = 1000
+)
+
 // insufficientNodesError is returned when a hashring does not
 // have enough nodes to satisfy a request for a node.
 type insufficientNodesError struct {
@@ -52,7 +69,7 @@ func (s SingleNodeHashring) GetN(_ string, _ *prompb.TimeSeries, n uint64) (stri
 	return string(s), nil
 }
 
-// simpleHashring represents a group of nodes handling write requests.
+// simpleHashring represents a group of nodes handling write requests by hashmoding individual series.
 type simpleHashring []string
 
 // Get returns a target to handle the given tenant and time series.
@@ -69,6 +86,81 @@ func (s simpleHashring) GetN(tenant string, ts *prompb.TimeSeries, n uint64) (st
 	return s[(labelpb.HashWithPrefix(tenant, ts.Labels)+n)%uint64(len(s))], nil
 }
 
+type section struct {
+	endpointIndex uint64
+	hash          uint64
+}
+
+type sections []section
+
+func (p sections) Len() int           { return len(p) }
+func (p sections) Less(i, j int) bool { return p[i].hash < p[j].hash }
+func (p sections) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+func (p sections) Sort()              { sort.Sort(p) }
+
+// consistentHashring represents a group of nodes handling write requests with consistent hashing.
+type consistentHashring struct {
+	endpoints    []string
+	sections     sections
+	numEndpoints uint64
+}
+
+func newConsistentHashring(endpoints []string, sectionsPerNode int) *consistentHashring {
+	// Replication works by choosing subsequent nodes in the ring.
+	// In order to improve consistency, we avoid relying on the ordering of the endpoints
+	// and sort them lexicographically.
+	sort.Strings(endpoints)
+
+	numSections := len(endpoints) * sectionsPerNode
+	ring := consistentHashring{
+		endpoints:    endpoints,
+		sections:     make(sections, 0, numSections),
+		numEndpoints: uint64(len(endpoints)),
+	}
+
+	hash := xxhash.New()
+	for endpointIndex, endpoint := range endpoints {
+		for i := 1; i <= sectionsPerNode; i++ {
+			_, _ = hash.Write([]byte(endpoint + ":" + strconv.Itoa(i)))
+			n := &section{
+				endpointIndex: uint64(endpointIndex),
+				hash:          hash.Sum64(),
+			}
+
+			ring.sections = append(ring.sections, *n)
+			hash.Reset()
+		}
+	}
+	sort.Sort(ring.sections)
+	return &ring
+}
+
+func (c consistentHashring) Get(tenant string, ts *prompb.TimeSeries) (string, error) {
+	return c.GetN(tenant, ts, 0)
+}
+
+func (c consistentHashring) GetN(tenant string, ts *prompb.TimeSeries, n uint64) (string, error) {
+	if n >= c.numEndpoints {
+		return "", &insufficientNodesError{have: c.numEndpoints, want: n + 1}
+	}
+
+	v := labelpb.HashWithPrefix(tenant, ts.Labels)
+
+	var i uint64
+	i = uint64(sort.Search(len(c.sections), func(i int) bool {
+		return c.sections[i].hash >= v
+	}))
+
+	numSections := uint64(len(c.sections))
+	if i == numSections {
+		i = 0
+	}
+
+	nodeIndex := (c.sections[i].endpointIndex + n) % c.numEndpoints
+
+	return c.endpoints[nodeIndex], nil
+}
+
 // multiHashring represents a set of hashrings.
 // Which hashring to use for a tenant is determined
 // by the tenants field of the hashring configuration.
@@ -121,13 +213,24 @@ func (m *multiHashring) GetN(tenant string, ts *prompb.TimeSeries, n uint64) (st
 // groups.
 // Which hashring to use for a tenant is determined
 // by the tenants field of the hashring configuration.
-func newMultiHashring(cfg []HashringConfig) Hashring {
+func newMultiHashring(algorithm HashringAlgorithm, cfg []HashringConfig) Hashring {
 	m := &multiHashring{
 		cache: make(map[string]Hashring),
 	}
 
+	newHashring := func(endpoints []string) Hashring {
+		switch algorithm {
+		case AlgorithmHashmod:
+			return simpleHashring(endpoints)
+		case AlgorithmConsistent:
+			return newConsistentHashring(endpoints, SectionsPerNode)
+		default:
+			return simpleHashring(endpoints)
+		}
+	}
+
 	for _, h := range cfg {
-		m.hashrings = append(m.hashrings, simpleHashring(h.Endpoints))
+		m.hashrings = append(m.hashrings, newHashring(h.Endpoints))
 		var t map[string]struct{}
 		if len(h.Tenants) != 0 {
 			t = make(map[string]struct{})
@@ -147,7 +250,7 @@ func newMultiHashring(cfg []HashringConfig) Hashring {
 // Which hashring to use for a tenant is determined
 // by the tenants field of the hashring configuration.
 // The updates chan is closed before exiting.
-func HashringFromConfigWatcher(ctx context.Context, updates chan<- Hashring, cw *ConfigWatcher) error {
+func HashringFromConfigWatcher(ctx context.Context, algorithm HashringAlgorithm, updates chan<- Hashring, cw *ConfigWatcher) error {
 	defer close(updates)
 	go cw.Run(ctx)
 
@@ -157,15 +260,15 @@ func HashringFromConfigWatcher(ctx context.Context, updates chan<- Hashring, cw
 			if !ok {
 				return errors.New("hashring config watcher stopped unexpectedly")
 			}
-			updates <- newMultiHashring(cfg)
+			updates <- newMultiHashring(algorithm, cfg)
 		case <-ctx.Done():
 			return ctx.Err()
 		}
 	}
 }
 
 // HashringFromConfig loads raw configuration content and returns a Hashring if the given configuration is not valid.
-func HashringFromConfig(content string) (Hashring, error) {
+func HashringFromConfig(algorithm HashringAlgorithm, content string) (Hashring, error) {
 	config, err := parseConfig([]byte(content))
 	if err != nil {
 		return nil, errors.Wrapf(err, "failed to parse configuration")
@@ -176,5 +279,5 @@ func HashringFromConfig(content string) (Hashring, error) {
 		return nil, errors.Wrapf(err, "failed to load configuration")
 	}
 
-	return newMultiHashring(config), err
+	return newMultiHashring(algorithm, config), err
 }