diff --git a/examples/binance-book/main.go b/examples/binance-book/main.go
index f9aa1288a..42d669a07 100644
--- a/examples/binance-book/main.go
+++ b/examples/binance-book/main.go
@@ -48,16 +48,8 @@ var rootCmd = &cobra.Command{
 		stream.SetPublicOnly()
 		stream.Subscribe(types.BookChannel, symbol, types.SubscribeOptions{})
 
-		stream.OnBookSnapshot(func(book types.SliceOrderBook) {
-			// log.Infof("book snapshot: %+v", book)
-		})
-
-		stream.OnBookUpdate(func(book types.SliceOrderBook) {
-			// log.Infof("book update: %+v", book)
-		})
-
-		streambook := types.NewStreamBook(symbol)
-		streambook.BindStream(stream)
+		streamBook := types.NewStreamBook(symbol)
+		streamBook.BindStream(stream)
 
 		go func() {
 			for {
@@ -66,8 +58,8 @@ var rootCmd = &cobra.Command{
 				case <-ctx.Done():
 					return
 
-				case <-streambook.C:
-					book := streambook.Copy()
+				case <-streamBook.C:
+					book := streamBook.Copy()
 
 					if valid, err := book.IsValid(); !valid {
 						log.Errorf("order book is invalid, error: %v", err)
diff --git a/pkg/exchange/binance/depthframe.go b/pkg/exchange/binance/depthframe.go
index 8129a3fbc..85223ce63 100644
--- a/pkg/exchange/binance/depthframe.go
+++ b/pkg/exchange/binance/depthframe.go
@@ -160,6 +160,18 @@ func (f *DepthFrame) PushEvent(e DepthEvent) {
 
 	// drop old events
 	if e.FinalUpdateID <= snapshot.FinalUpdateID {
+		log.Infof("DROP %s depth update event, updateID %d ~ %d (len %d)",
+			f.Symbol,
+			e.FirstUpdateID, e.FinalUpdateID, e.FinalUpdateID-e.FirstUpdateID)
+		return
+	}
+
+	if e.FirstUpdateID > snapshot.FinalUpdateID+1 {
+		log.Infof("MISSING %s depth update event, resetting, updateID %d ~ %d (len %d)",
+			f.Symbol,
+			e.FirstUpdateID, e.FinalUpdateID, e.FinalUpdateID-e.FirstUpdateID)
+
+		f.reset()
 		return
 	}
 
@@ -181,6 +193,7 @@ func (f *DepthFrame) fetch(ctx context.Context) (*DepthEvent, error) {
 	}
 
 	event := DepthEvent{
+		Symbol:        f.Symbol,
 		FirstUpdateID: 0,
 		FinalUpdateID: response.LastUpdateID,
 	}
diff --git a/pkg/exchange/binance/parse.go b/pkg/exchange/binance/parse.go
index b669b0b7b..9cc7f51f9 100644
--- a/pkg/exchange/binance/parse.go
+++ b/pkg/exchange/binance/parse.go
@@ -56,14 +56,14 @@ executionReport
 type ExecutionReportEvent struct {
 	EventBase
 
-	Symbol        string `json:"s"`
-	Side          string `json:"S"`
+	Symbol string `json:"s"`
+	Side   string `json:"S"`
 
 	ClientOrderID         string `json:"c"`
 	OriginalClientOrderID string `json:"C"`
 
 	OrderType         string `json:"o"`
-	OrderCreationTime int64 `json:"O"`
+	OrderCreationTime int64  `json:"O"`
 
 	TimeInForce     string `json:"f"`
 	IcebergQuantity string `json:"F"`
@@ -71,13 +71,13 @@ type ExecutionReportEvent struct {
 	OrderQuantity      string `json:"q"`
 	QuoteOrderQuantity string `json:"Q"`
 
-	OrderPrice    string `json:"p"`
-	StopPrice     string `json:"P"`
+	OrderPrice string `json:"p"`
+	StopPrice  string `json:"P"`
 
 	IsOnBook bool `json:"w"`
 
-	IsMaker  bool `json:"m"`
-	Ignore   bool `json:"M"`
+	IsMaker bool `json:"m"`
+	Ignore  bool `json:"M"`
 
 	CommissionAmount string `json:"n"`
 	CommissionAsset  string `json:"N"`
@@ -319,17 +319,40 @@ type DepthEvent struct {
 	Asks []DepthEntry
 }
 
+func (e *DepthEvent) String() (o string) {
+	o += fmt.Sprintf("Depth %s bid/ask = ", e.Symbol)
+
+	if len(e.Bids) == 0 {
+		o += "empty"
+	} else {
+		o += e.Bids[0].PriceLevel
+	}
+
+	o += "/"
+
+	if len(e.Asks) == 0 {
+		o += "empty"
+	} else {
+		o += e.Asks[0].PriceLevel
+	}
+
+	o += fmt.Sprintf(" %d ~ %d", e.FirstUpdateID, e.FinalUpdateID)
+	return o
+}
+
 func (e *DepthEvent) OrderBook() (book types.SliceOrderBook, err error) {
 	book.Symbol = e.Symbol
 
 	for _, entry := range e.Bids {
 		quantity, err := fixedpoint.NewFromString(entry.Quantity)
 		if err != nil {
+			log.WithError(err).Errorf("depth quantity parse error: %s", entry.Quantity)
 			continue
 		}
 
 		price, err := fixedpoint.NewFromString(entry.PriceLevel)
 		if err != nil {
+			log.WithError(err).Errorf("depth price parse error: %s", entry.PriceLevel)
 			continue
 		}
 
@@ -344,11 +367,13 @@ func (e *DepthEvent) OrderBook() (book types.SliceOrderBook, err error) {
 	for _, entry := range e.Asks {
 		quantity, err := fixedpoint.NewFromString(entry.Quantity)
 		if err != nil {
+			log.WithError(err).Errorf("depth quantity parse error: %s", entry.Quantity)
 			continue
 		}
 
 		price, err := fixedpoint.NewFromString(entry.PriceLevel)
 		if err != nil {
+			log.WithError(err).Errorf("depth price parse error: %s", entry.PriceLevel)
 			continue
 		}
 
@@ -360,7 +385,7 @@ func (e *DepthEvent) OrderBook() (book types.SliceOrderBook, err error) {
 		book.Asks = book.Asks.Upsert(pv, false)
 	}
 
-	return
+	return book, nil
 }
 
 func parseDepthEntry(val *fastjson.Value) (*DepthEntry, error) {
diff --git a/pkg/exchange/binance/stream.go b/pkg/exchange/binance/stream.go
index 41fe47f26..73664afb6 100644
--- a/pkg/exchange/binance/stream.go
+++ b/pkg/exchange/binance/stream.go
@@ -75,7 +75,7 @@ func NewStream(client *binance.Client) *Stream {
 
 	stream.OnDepthEvent(func(e *DepthEvent) {
 		if debugBinanceDepth {
-			log.Infof("received %s depth event updateID %d~%d (len %d)", e.Symbol, e.FirstUpdateID, e.FinalUpdateID, e.FinalUpdateID-e.FirstUpdateID)
+			log.Infof("received %s depth event updateID %d ~ %d (len %d)", e.Symbol, e.FirstUpdateID, e.FinalUpdateID, e.FinalUpdateID-e.FirstUpdateID)
 		}
 
 		f, ok := stream.depthFrames[e.Symbol]
@@ -88,27 +88,29 @@ func NewStream(client *binance.Client) *Stream {
 
 			stream.depthFrames[e.Symbol] = f
 
-			f.OnReady(func(e DepthEvent, bufEvents []DepthEvent) {
-				snapshot, err := e.OrderBook()
+			f.OnReady(func(snapshotDepth DepthEvent, bufEvents []DepthEvent) {
+				log.Infof("depth snapshot: %s", snapshotDepth.String())
+
+				snapshot, err := snapshotDepth.OrderBook()
 				if err != nil {
 					log.WithError(err).Error("book snapshot convert error")
 					return
 				}
 
 				if valid, err := snapshot.IsValid(); !valid {
-					log.Warnf("depth snapshot is invalid, event: %+v, error: %v", e, err)
+					log.Errorf("depth snapshot is invalid, event: %+v, error: %v", snapshotDepth, err)
 				}
 
 				stream.EmitBookSnapshot(snapshot)
 
 				for _, e := range bufEvents {
-					book, err := e.OrderBook()
+					bookUpdate, err := e.OrderBook()
 					if err != nil {
 						log.WithError(err).Error("book convert error")
 						return
 					}
 
-					stream.EmitBookUpdate(book)
+					stream.EmitBookUpdate(bookUpdate)
 				}
 			})
 
@@ -185,7 +187,7 @@ func NewStream(client *binance.Client) *Stream {
 	})
 
 	stream.OnDisconnect(func() {
-		log.Infof("resetting depth snapshot...")
+		log.Infof("resetting depth snapshots...")
 		for _, f := range stream.depthFrames {
 			f.reset()
 		}
diff --git a/pkg/types/orderbook.go b/pkg/types/orderbook.go
index 8b7f30feb..b5e5602c5 100644
--- a/pkg/types/orderbook.go
+++ b/pkg/types/orderbook.go
@@ -52,6 +52,27 @@ func NewMutexOrderBook(symbol string) *MutexOrderBook {
 	}
 }
 
+func (b *MutexOrderBook) IsValid() (ok bool, err error) {
+	b.Lock()
+	ok, err = b.OrderBook.IsValid()
+	b.Unlock()
+	return ok, err
+}
+
+func (b *MutexOrderBook) BestBid() (pv PriceVolume, ok bool) {
+	b.Lock()
+	pv, ok = b.OrderBook.BestBid()
+	b.Unlock()
+	return pv, ok
+}
+
+func (b *MutexOrderBook) BestAsk() (pv PriceVolume, ok bool) {
+	b.Lock()
+	pv, ok = b.OrderBook.BestAsk()
+	b.Unlock()
+	return pv, ok
+}
+
 func (b *MutexOrderBook) Load(book SliceOrderBook) {
 	b.Lock()
 	b.OrderBook.Load(book)
@@ -66,14 +87,16 @@ func (b *MutexOrderBook) Reset() {
 
 func (b *MutexOrderBook) CopyDepth(depth int) OrderBook {
 	b.Lock()
-	defer b.Unlock()
-	return b.OrderBook.CopyDepth(depth)
+	book := b.OrderBook.CopyDepth(depth)
+	b.Unlock()
+	return book
 }
 
 func (b *MutexOrderBook) Copy() OrderBook {
 	b.Lock()
-	defer b.Unlock()
-	return b.OrderBook.Copy()
+	book := b.OrderBook.Copy()
+	b.Unlock()
+	return book
 }
 
 func (b *MutexOrderBook) Update(update SliceOrderBook) {
diff --git a/pkg/types/sliceorderbook.go b/pkg/types/sliceorderbook.go
index 813e73fd1..24f1339d5 100644
--- a/pkg/types/sliceorderbook.go
+++ b/pkg/types/sliceorderbook.go
@@ -93,10 +93,10 @@ func (b *SliceOrderBook) PriceVolumesBySide(side SideType) PriceVolumeSlice {
 	switch side {
 
 	case SideTypeBuy:
-		return b.Bids
+		return b.Bids.Copy()
 
 	case SideTypeSell:
-		return b.Asks
+		return b.Asks.Copy()
 	}
 
 	return nil
@@ -122,11 +122,6 @@ func (b *SliceOrderBook) updateBids(pvs PriceVolumeSlice) {
 	}
 }
 
-func (b *SliceOrderBook) load(book SliceOrderBook) {
-	b.Reset()
-	b.update(book)
-}
-
 func (b *SliceOrderBook) update(book SliceOrderBook) {
 	b.updateBids(book.Bids)
 	b.updateAsks(book.Asks)
@@ -138,7 +133,8 @@ func (b *SliceOrderBook) Reset() {
 }
 
 func (b *SliceOrderBook) Load(book SliceOrderBook) {
-	b.load(book)
+	b.Reset()
+	b.update(book)
 	b.EmitLoad(b)
 }