infoschema: change sieve Get() function Mutex to RWMutex (#58243)

close pingcap/tidb#58227

pkg/infoschema/sieve.go

@@ -18,6 +18,7 @@ import (
 	"container/list"
 	"context"
 	"sync"
+	"sync/atomic"
 
 	"github.com/pingcap/failpoint"
 	"github.com/pingcap/tidb/pkg/infoschema/internal"
@@ -27,7 +28,7 @@ import (
 type entry[K comparable, V any] struct {
 	key     K
 	value   V
-	visited bool
+	visited atomic.Bool
 	element *list.Element
 	size    uint64
 }
@@ -48,7 +49,7 @@ func (t *entry[K, V]) Size() uint64 {
 type Sieve[K comparable, V any] struct {
 	ctx    context.Context
 	cancel context.CancelFunc
-	mu     sync.Mutex
+	mu     sync.RWMutex
 	size   uint64
 	// capacity can be set to zero for disabling infoschema v2
 	capacity uint64
@@ -132,7 +133,7 @@ func (s *Sieve[K, V]) Set(key K, value V) {
 
 	if e, ok := s.items[key]; ok {
 		e.value = value
-		e.visited = true
+		e.visited.Store(true)
 		return
 	}
 
@@ -156,10 +157,13 @@ func (s *Sieve[K, V]) Get(key K) (value V, ok bool) {
 		var v V
 		failpoint.Return(v, false)
 	})
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	if e, ok := s.items[key]; ok {
-		e.visited = true
+
+	s.mu.RLock()
+	e, ok := s.items[key]
+	s.mu.RUnlock()
+
+	if ok {
+		e.visited.Store(true)
 		s.hook.onHit()
 		return e.value, true
 	}
@@ -254,8 +258,8 @@ func (s *Sieve[K, V]) evict() {
 		panic("sieve: evicting non-existent element")
 	}
 
-	for el.visited {
-		el.visited = false
+	for el.visited.Load() {
+		el.visited.Store(false)
 		o = o.Prev()
 		if o == nil {
 			o = s.ll.Back()

pkg/infoschema/sieve_test.go

@@ -15,6 +15,9 @@
 package infoschema
 
 import (
+	"context"
+	"math/rand"
+	"sync/atomic"
 	"testing"
 
 	"github.com/pingcap/tidb/pkg/util/size"
@@ -135,3 +138,43 @@ func TestPurge(t *testing.T) {
 
 	cache.Close()
 }
+
+func BenchmarkSieveGet(b *testing.B) {
+	c := newSieve[int, int](8192)
+	ent := make([]int, b.N)
+	for i := 0; i < b.N; i++ {
+		var k int
+		if i%2 == 0 {
+			k = int(rand.Int63() % 16384)
+		} else {
+			k = int(rand.Int63() % 32768)
+		}
+		c.Set(k, k)
+		ent[i] = k
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		for {
+			v := int(rand.Int63() % 8192)
+			c.Set(v, v)
+			if ctx.Err() != nil {
+				return
+			}
+		}
+	}()
+
+	b.ResetTimer()
+
+	var hit, miss int64
+	for i := 0; i < b.N; i++ {
+		if _, ok := c.Get(ent[i]); ok {
+			atomic.AddInt64(&hit, 1)
+		} else {
+			atomic.AddInt64(&miss, 1)
+		}
+	}
+
+	b.Logf("%d: hit %d, miss %d, ratio %4.2f", b.N, hit, miss, float64(hit)/float64(hit+miss))
+	cancel()
+}