add a Resize method to 2Q

2q.go

@@ -30,8 +30,10 @@ const (
 // head. The ARCCache is similar, but does not require setting any
 // parameters.
 type TwoQueueCache[K comparable, V any] struct {
-	size       int
-	recentSize int
+	size        int
+	recentSize  int
+	recentRatio float64
+	ghostRatio  float64
 
 	recent      simplelru.LRUCache[K, V]
 	frequent    simplelru.LRUCache[K, V]
@@ -80,6 +82,8 @@ func New2QParams[K comparable, V any](size int, recentRatio, ghostRatio float64)
 	c := &TwoQueueCache[K, V]{
 		size:        size,
 		recentSize:  recentSize,
+		recentRatio: recentRatio,
+		ghostRatio:  ghostRatio,
 		recent:      recent,
 		frequent:    frequent,
 		recentEvict: recentEvict,
@@ -171,6 +175,34 @@ func (c *TwoQueueCache[K, V]) Len() int {
 	return c.recent.Len() + c.frequent.Len()
 }
 
+// Resize changes the cache size.
+func (c *TwoQueueCache[K, V]) Resize(size int) (evicted int) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	// Recalculate the sub-sizes
+	recentSize := int(float64(size) * c.recentRatio)
+	evictSize := int(float64(size) * c.ghostRatio)
+	c.size = size
+	c.recentSize = recentSize
+
+	// ensureSpace
+	diff := c.recent.Len() + c.frequent.Len() - size
+	if diff < 0 {
+		diff = 0
+	}
+	for i := 0; i < diff; i++ {
+		c.ensureSpace(true)
+	}
+
+	// Reallocate the LRUs
+	c.recent.Resize(size)
+	c.frequent.Resize(size)
+	c.recentEvict.Resize(evictSize)
+
+	return diff
+}
+
 // Keys returns a slice of the keys in the cache.
 // The frequently used keys are first in the returned slice.
 func (c *TwoQueueCache[K, V]) Keys() []K {

2q_test.go

@@ -218,6 +218,75 @@ func Test2Q_Add_RecentEvict(t *testing.T) {
 	}
 }
 
+func Test2Q_Resize(t *testing.T) {
+	l, err := New2Q[int, int](100)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	// Touch all the entries, should be in t1
+	for i := 0; i < 100; i++ {
+		l.Add(i, i)
+	}
+
+	evicted := l.Resize(50)
+	if evicted != 50 {
+		t.Fatalf("bad: %d", evicted)
+	}
+
+	if n := l.recent.Len(); n != 50 {
+		t.Fatalf("bad: %d", n)
+	}
+	if n := l.frequent.Len(); n != 0 {
+		t.Fatalf("bad: %d", n)
+	}
+
+	l, err = New2Q[int, int](100)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	for i := 0; i < 100; i++ {
+		l.Add(i, i)
+	}
+
+	for i := 0; i < 50; i++ {
+		l.Add(i, i)
+	}
+
+	evicted = l.Resize(50)
+	if evicted != 50 {
+		t.Fatalf("bad: %d", evicted)
+	}
+
+	if n := l.recent.Len(); n != 12 {
+		t.Fatalf("bad: %d", n)
+	}
+	if n := l.frequent.Len(); n != 38 {
+		t.Fatalf("bad: %d", n)
+	}
+
+	l, err = New2Q[int, int](100)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	for i := 0; i < 100; i++ {
+		l.Add(i, i)
+		l.Add(i, i)
+	}
+
+	evicted = l.Resize(50)
+	if evicted != 50 {
+		t.Fatalf("bad: %d", evicted)
+	}
+
+	if n := l.recent.Len(); n != 0 {
+		t.Fatalf("bad: %d", n)
+	}
+	if n := l.frequent.Len(); n != 50 {
+		t.Fatalf("bad: %d", n)
+	}
+}
+
 func Test2Q(t *testing.T) {
 	l, err := New2Q[int, int](128)
 	if err != nil {