[db] ResetSnapshots() performance improvement

db/batch/batch_impl.go

@@ -27,7 +27,7 @@
 		tag          int            // latest snapshot + 1
 		batchShots   []int          // snapshots of batch are merely size of write queue at time of snapshot
 		caches       []KVStoreCache // snapshots of cache
-		keyTags      map[kvCacheKey][]int
+		keyTags      map[kvCacheKey]*kvCacheValue
 		tagKeys      [][]kvCacheKey
 	}
 )
@@ -254,19 +254,19 @@
 	cb.tag = 0
 	cb.batchShots = make([]int, 0)
 	cb.caches = []KVStoreCache{NewKVCache()}
-	cb.keyTags = map[kvCacheKey][]int{}
+	cb.keyTags = map[kvCacheKey]*kvCacheValue{}
 	cb.tagKeys = [][]kvCacheKey{{}}
 }
 
 func (cb *cachedBatch) touchKey(h kvCacheKey) {
 	tags, ok := cb.keyTags[h]
 	if !ok {
-		cb.keyTags[h] = []int{cb.tag}
+		cb.keyTags[h] = newkvCacheValue([]int{cb.tag})
 		cb.tagKeys[cb.tag] = append(cb.tagKeys[cb.tag], h)
 		return
 	}
-	if tags[len(tags)-1] != cb.tag {
-		cb.keyTags[h] = append(tags, cb.tag)
+	if tags.last() != cb.tag {
+		tags.append(cb.tag)
 		cb.tagKeys[cb.tag] = append(cb.tagKeys[cb.tag], h)
 	}
 }
@@ -306,8 +306,8 @@
 	var v []byte
 	err := ErrNotExist
 	if tags, ok := cb.keyTags[h]; ok {
-		for i := len(tags) - 1; i >= 0; i-- {
-			v, err = cb.caches[tags[i]].Read(&h)
+		for i := tags.len() - 1; i >= 0; i-- {
+			v, err = cb.caches[tags.getAt(i)].Read(&h)
 			if errors.Cause(err) == ErrNotExist {
 				continue
 			}
@@ -344,8 +344,9 @@
 	for tag := cb.tag; tag < len(cb.tagKeys); tag++ {
 		keys := cb.tagKeys[tag]
 		for _, key := range keys {
-			cb.keyTags[key] = cb.keyTags[key][:len(cb.keyTags[key])-1]
-			if len(cb.keyTags[key]) == 0 {
+			kv := cb.keyTags[key]
+			kv.reverse()
+			if kv.len() == 0 {
 				delete(cb.keyTags, key)
 			}
 		}
@@ -369,12 +370,10 @@
 		cb.caches = cb.caches[:1]
 	}
 	keys := make([]kvCacheKey, 0, len(cb.keyTags))
-	for key := range cb.keyTags {
+	for key, v := range cb.keyTags {
+		v.reset()
 		keys = append(keys, key)
 	}
-	for _, key := range keys {
-		cb.keyTags[key] = []int{0}
-	}
 	cb.tagKeys = [][]kvCacheKey{keys}
 }
 

db/batch/kv_cache.go

@@ -27,6 +27,7 @@ type (
 		key1 string
 		key2 string
 	}
+	kvCacheValue []int
 
 	node struct {
 		value   []byte
@@ -39,6 +40,38 @@ type (
 	}
 )
 
+func newkvCacheValue(v []int) *kvCacheValue {
+	return (*kvCacheValue)(&v)
+}
+
+func (kv *kvCacheValue) reset() {
+	([]int)(*kv)[0] = 0
+	*kv = (*kv)[0:1]
+}
+
+func (kv *kvCacheValue) reverse() {
+	*kv = (*kv)[0 : kv.len()-1]
+}
+func (kv *kvCacheValue) get() []int {
+	return ([]int)(*kv)
+}
+
+func (kv *kvCacheValue) getAt(i int) int {
+	return ([]int)(*kv)[i]
+}
+
+func (kv *kvCacheValue) append(v int) {
+	*kv = append(*kv, v)
+}
+
+func (kv *kvCacheValue) len() int {
+	return len(*kv)
+}
+
+func (kv *kvCacheValue) last() int {
+	return (*kv)[len(*kv)-1]
+}
+
 // NewKVCache returns a KVCache
 func NewKVCache() KVStoreCache {
 	return &kvCache{

db/batch/kv_cache_test.go

@@ -95,6 +95,26 @@ func TestKvCache(t *testing.T) {
 	require.Equal(v, v3)
 }
 
+func TestKvCacheValue(t *testing.T) {
+	require := require.New(t)
+
+	c := newkvCacheValue([]int{1})
+	require.Equal([]int{1}, c.get())
+	require.Equal(1, c.len())
+
+	c.reset()
+	require.Equal([]int{0}, c.get())
+
+	c.append(3)
+	require.Equal([]int{0, 3}, c.get())
+	require.Equal(0, c.getAt(0))
+	require.Equal(3, c.last())
+	require.Equal(2, c.len())
+	c.reverse()
+	require.Equal([]int{0}, c.get())
+	require.Equal(1, c.len())
+}
+
 func TestWriteIfNotExist(t *testing.T) {
 	require := require.New(t)
 
@@ -114,3 +134,37 @@ func TestWriteIfNotExist(t *testing.T) {
 	err = c.WriteIfNotExist(k1, v1)
 	require.NoError(err)
 }
+
+func BenchmarkMapKey_ValueOperate(b *testing.B) {
+	keyTags := map[kvCacheKey]*kvCacheValue{}
+	keyTags2 := map[kvCacheKey][]int{}
+	for i := 0; i < 10000; i++ {
+		key := kvCacheKey{
+			key1: string(make([]byte, 5)),
+			key2: string(make([]byte, 32)),
+		}
+		keyTags[key] = newkvCacheValue([]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9})
+		keyTags2[key] = []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
+	}
+	b.Run("reset by map key", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			for k := range keyTags {
+				keyTags[k].reset()
+			}
+		}
+	})
+	b.Run("reset by map value, 2x faster", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			for _, v := range keyTags {
+				v.reset()
+			}
+		}
+	})
+	b.Run("orign map assign", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			for k := range keyTags2 {
+				keyTags2[k] = []int{0}
+			}
+		}
+	})
+}