added Close() method to KVBatch interface

index/store/batch.go

@@ -51,3 +51,7 @@ func (b *EmulatedBatch) Merge(key, val []byte) {
 func (b *EmulatedBatch) Reset() {
 	b.Ops = b.Ops[:0]
 }
+
+func (b *EmulatedBatch) Close() error {
+	return nil
+}

index/store/goleveldb/batch.go

@@ -36,3 +36,10 @@ func (b *Batch) Reset() {
 	b.batch.Reset()
 	b.merge = store.NewEmulatedMerge(b.store.mo)
 }
+
+func (b *Batch) Close() error {
+	b.batch.Reset()
+	b.batch = nil
+	b.merge = nil
+	return nil
+}

index/store/kvstore.go

@@ -118,4 +118,7 @@ type KVBatch interface {
 
 	// Reset frees resources for this batch and allows reuse
 	Reset()
+
+	// Close frees resources
+	Close() error
 }

index/store/metrics/batch.go

@@ -24,3 +24,9 @@ func (b *Batch) Merge(key, val []byte) {
 func (b *Batch) Reset() {
 	b.o.Reset()
 }
+
+func (b *Batch) Close() error {
+	err := b.o.Close()
+	b.o = nil
+	return err
+}

index/store/null/null.go

@@ -84,6 +84,7 @@ func (i *batch) Set(key, val []byte)   {}
 func (i *batch) Delete(key []byte)     {}
 func (i *batch) Merge(key, val []byte) {}
 func (i *batch) Reset()                {}
+func (i *batch) Close() error          { return nil }
 
 type writer struct{}