[Chore] Use only one shard

README.md

@@ -75,11 +75,6 @@ func main() {
         panic(err)
     }
 
-    // ShardCount sets the number of cache shards to 256.
-    // The number of shards must always be a degree of two.
-    // Default is 128.
-    builder.ShardCount(256)
-
     // StatsEnabled determines whether statistics should be calculated when the cache is running.
     // By default, statistics calculating is disabled.
     builder.StatsEnabled(true)

builder.go

@@ -3,35 +3,24 @@ package otter
 import "errors"
 
 const (
-	defaultShardCount   = 128
 	defaultStatsEnabled = false
 )
 
-var (
-	ErrIllegalCapacity   = errors.New("capacity should be positive")
-	ErrIllegalShardCount = errors.New("hashtable count should be positive")
-)
+var ErrIllegalCapacity = errors.New("capacity should be positive")
 
 type options[K comparable, V any] struct {
 	capacity     int
-	shardCount   int
 	statsEnabled bool
 	costFunc     func(key K, value V) uint32
 }
 
 func (o *options[K, V]) validate() error {
-	// shard count should be power of two.
-	if o.shardCount <= 0 || (o.shardCount&(o.shardCount-1)) != 0 {
-		return ErrIllegalShardCount
-	}
-
 	return nil
 }
 
 func (o *options[K, V]) toConfig() Config[K, V] {
 	return Config[K, V]{
 		Capacity:     o.capacity,
-		ShardCount:   o.shardCount,
 		StatsEnabled: o.statsEnabled,
 		CostFunc:     o.costFunc,
 	}
@@ -57,7 +46,6 @@ func NewBuilder[K comparable, V any](capacity int) (*Builder[K, V], error) {
 	return &Builder[K, V]{
 		options: options[K, V]{
 			capacity:     capacity,
-			shardCount:   defaultShardCount,
 			statsEnabled: defaultStatsEnabled,
 			costFunc: func(key K, value V) uint32 {
 				return 1
@@ -66,11 +54,6 @@ func NewBuilder[K comparable, V any](capacity int) (*Builder[K, V], error) {
 	}, nil
 }
 
-func (b *Builder[K, V]) ShardCount(shardCount int) *Builder[K, V] {
-	b.shardCount = shardCount
-	return b
-}
-
 func (b *Builder[K, V]) StatsEnabled(statsEnabled bool) *Builder[K, V] {
 	b.statsEnabled = statsEnabled
 	return b

builder_test.go

@@ -24,20 +24,10 @@ func TestBuilder_NewFailed(t *testing.T) {
 	}
 }
 
-func TestBuilder_BuildFailed(t *testing.T) {
-	b := MustBuilder[int, int](10)
-
-	_, err := b.ShardCount(129).Build()
-	if err == nil || !errors.Is(err, ErrIllegalShardCount) {
-		t.Fatalf("should fail with an error %v, but got %v", ErrIllegalShardCount, err)
-	}
-}
-
 func TestBuilder_BuildSuccess(t *testing.T) {
 	b := MustBuilder[int, int](10)
 
 	c, err := b.
-		ShardCount(256).
 		StatsEnabled(true).
 		Cost(func(key int, value int) uint32 {
 			return 2

cache.go

@@ -23,49 +23,48 @@ func zeroValue[V any]() V {
 
 type Config[K comparable, V any] struct {
 	Capacity     int
-	ShardCount   int
 	StatsEnabled bool
 	CostFunc     func(key K, value V) uint32
 }
 
 type Cache[K comparable, V any] struct {
-	shards       []*hashtable.Map[K, V]
+	hashmap      *hashtable.Map[K, V]
 	policy       *s3fifo.Policy[K, V]
 	expirePolicy *expire.Policy[K, V]
 	stats        *stats.Stats
 	readBuffers  []*lossy.Buffer[node.Node[K, V]]
 	writeBuffer  *queue.MPSC[node.WriteTask[K, V]]
 	closeOnce    sync.Once
 	doneClear    chan struct{}
-	hasher       *hasher[K]
 	costFunc     func(key K, value V) uint32
-	mask         uint64
 	capacity     int
+	mask         uint32
 }
 
 func NewCache[K comparable, V any](c Config[K, V]) *Cache[K, V] {
-	shards := make([]*hashtable.Map[K, V], 0, c.ShardCount)
-	readBuffers := make([]*lossy.Buffer[node.Node[K, V]], 0, c.ShardCount)
-	for i := 0; i < c.ShardCount; i++ {
-		shards = append(shards, hashtable.New[K, V]())
+	parallelism := xruntime.Parallelism()
+	roundedParallelism := int(xmath.RoundUpPowerOf2(parallelism))
+	writeBufferCapacity := 128 * roundedParallelism
+	readBuffersCount := 4 * roundedParallelism
+
+	readBuffers := make([]*lossy.Buffer[node.Node[K, V]], 0, readBuffersCount)
+	for i := 0; i < readBuffersCount; i++ {
 		readBuffers = append(readBuffers, lossy.New[node.Node[K, V]]())
 	}
 
-	writeBufferCapacity := 128 * int(xmath.RoundUpPowerOf2(xruntime.Parallelism()))
 	cache := &Cache[K, V]{
-		shards:      shards,
+		hashmap:     hashtable.New[K, V](),
 		policy:      s3fifo.NewPolicy[K, V](uint32(c.Capacity)),
 		readBuffers: readBuffers,
 		writeBuffer: queue.NewMPSC[node.WriteTask[K, V]](writeBufferCapacity),
 		doneClear:   make(chan struct{}),
-		hasher:      newHasher[K](),
-		mask:        uint64(c.ShardCount - 1),
+		mask:        uint32(readBuffersCount - 1),
 		costFunc:    c.CostFunc,
 		capacity:    c.Capacity,
 	}
 
 	cache.expirePolicy = expire.NewPolicy[K, V](func(n *node.Node[K, V]) {
-		cache.shards[cache.getShardIdx(n.Key())].EvictNode(n)
+		cache.hashmap.EvictNode(n)
 	})
 	if c.StatsEnabled {
 		cache.stats = stats.New()
@@ -77,8 +76,8 @@ func NewCache[K comparable, V any](c Config[K, V]) *Cache[K, V] {
 	return cache
 }
 
-func (c *Cache[K, V]) getShardIdx(key K) int {
-	return int(c.hasher.hash(key) & c.mask)
+func (c *Cache[K, V]) getReadBufferIdx() int {
+	return int(xruntime.Fastrand() & c.mask)
 }
 
 func (c *Cache[K, V]) Has(key K) bool {
@@ -87,8 +86,7 @@ func (c *Cache[K, V]) Has(key K) bool {
 }
 
 func (c *Cache[K, V]) Get(key K) (V, bool) {
-	idx := c.getShardIdx(key)
-	got, ok := c.shards[idx].Get(key)
+	got, ok := c.hashmap.Get(key)
 	if !ok {
 		c.stats.IncMisses()
 		return zeroValue[V](), false
@@ -100,18 +98,19 @@ func (c *Cache[K, V]) Get(key K) (V, bool) {
 		return zeroValue[V](), false
 	}
 
-	c.afterGet(idx, got)
+	c.afterGet(got)
 	c.stats.IncHits()
 
 	return got.Value(), ok
 }
 
-func (c *Cache[K, V]) afterGet(idx int, got *node.Node[K, V]) {
+func (c *Cache[K, V]) afterGet(got *node.Node[K, V]) {
+	idx := c.getReadBufferIdx()
 	pb := c.readBuffers[idx].Add(got)
 	if pb != nil {
 		deleted := c.policy.Read(pb.Deleted, pb.Returned)
 		for _, n := range deleted {
-			c.shards[c.getShardIdx(n.Key())].EvictNode(n)
+			c.hashmap.EvictNode(n)
 		}
 		c.readBuffers[idx].Free()
 	}
@@ -133,9 +132,7 @@ func (c *Cache[K, V]) set(key K, value V, expiration uint64) {
 		return
 	}
 
-	idx := c.getShardIdx(key)
-	s := c.shards[idx]
-	got, ok := s.Get(key)
+	got, ok := c.hashmap.Get(key)
 	if ok {
 		if !got.IsExpired() {
 			oldCost := got.SwapCost(cost)
@@ -152,7 +149,7 @@ func (c *Cache[K, V]) set(key K, value V, expiration uint64) {
 	}
 
 	n := node.New(key, value, expiration, cost)
-	evicted := s.Set(n)
+	evicted := c.hashmap.Set(n)
 	// TODO: try insert?
 	c.writeBuffer.Insert(node.NewAddTask(n))
 	if evicted != nil {
@@ -161,7 +158,7 @@ func (c *Cache[K, V]) set(key K, value V, expiration uint64) {
 }
 
 func (c *Cache[K, V]) Delete(key K) {
-	deleted := c.shards[c.getShardIdx(key)].Delete(key)
+	deleted := c.hashmap.Delete(key)
 	if deleted != nil {
 		c.writeBuffer.Insert(node.NewDeleteTask(deleted))
 	}
@@ -202,7 +199,7 @@ func (c *Cache[K, V]) process() {
 
 			d := c.policy.Write(deleted, e, buffer)
 			for _, n := range d {
-				c.shards[c.getShardIdx(n.Key())].EvictNode(n)
+				c.hashmap.EvictNode(n)
 			}
 
 			buffer = buffer[:0]
@@ -217,8 +214,8 @@ func (c *Cache[K, V]) Clear() {
 }
 
 func (c *Cache[K, V]) clear(task node.WriteTask[K, V]) {
-	for i := 0; i < len(c.shards); i++ {
-		c.shards[i].Clear()
+	c.hashmap.Clear()
+	for i := 0; i < len(c.readBuffers); i++ {
 		c.readBuffers[i].Clear()
 	}
 

go.mod

@@ -6,11 +6,6 @@ require (
 	github.com/dolthub/maphash v0.1.0
 	github.com/dolthub/swiss v0.2.1
 	github.com/gammazero/deque v0.2.1
-	github.com/zeebo/xxh3 v1.0.2
 )
 
-require (
-	github.com/klauspost/cpuid/v2 v2.2.6 // indirect
-	github.com/stretchr/testify v1.8.2 // indirect
-	golang.org/x/sys v0.15.0 // indirect
-)
+require github.com/stretchr/testify v1.8.2 // indirect

go.sum

@@ -7,8 +7,6 @@ github.com/dolthub/swiss v0.2.1 h1:gs2osYs5SJkAaH5/ggVJqXQxRXtWshF6uE0lgR/Y3Gw=
 github.com/dolthub/swiss v0.2.1/go.mod h1:8AhKZZ1HK7g18j7v7k6c5cYIGEZJcPn0ARsai8cUrh0=
 github.com/gammazero/deque v0.2.1 h1:qSdsbG6pgp6nL7A0+K/B7s12mcCY/5l5SIUpMOl+dC0=
 github.com/gammazero/deque v0.2.1/go.mod h1:LFroj8x4cMYCukHJDbxFCkT+r9AndaJnFMuZDV34tuU=
-github.com/klauspost/cpuid/v2 v2.2.6 h1:ndNyv040zDGIDh8thGkXYjnFtiN02M1PVVF+JE/48xc=
-github.com/klauspost/cpuid/v2 v2.2.6/go.mod h1:Lcz8mBdAVJIBVzewtcLocK12l3Y+JytZYpaMropDUws=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -18,12 +16,6 @@ github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.8.2 h1:+h33VjcLVPDHtOdpUCuF+7gSuG3yGIftsP1YvFihtJ8=
 github.com/stretchr/testify v1.8.2/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
-github.com/zeebo/assert v1.3.0 h1:g7C04CbJuIDKNPFHmsk4hwZDO5O+kntRxzaUoNXj+IQ=
-github.com/zeebo/xxh3 v1.0.2 h1:xZmwmqxHZA8AI603jOQ0tMqmBr9lPeFwGg6d+xy9DC0=
-github.com/zeebo/xxh3 v1.0.2/go.mod h1:5NWz9Sef7zIDm2JHfFlcQvNekmcEl9ekUZQQKCYaDcA=
-golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.15.0 h1:h48lPFYpsTvQJZF4EKyI4aLHaev3CxivZmv7yZig9pc=
-golang.org/x/sys v0.15.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=