diff --git a/examples/binance-book/main.go b/examples/binance-book/main.go
index ff89b33c7..9823bc454 100644
--- a/examples/binance-book/main.go
+++ b/examples/binance-book/main.go
@@ -49,15 +49,36 @@ var rootCmd = &cobra.Command{
 		stream.Subscribe(types.BookChannel, symbol, types.SubscribeOptions{})
 
 		stream.OnBookSnapshot(func(book types.OrderBook) {
-			log.Infof("book snapshot: %+v", book)
+			// log.Infof("book snapshot: %+v", book)
 		})
 
 		stream.OnBookUpdate(func(book types.OrderBook) {
-			log.Infof("book update: %+v", book)
+			// log.Infof("book update: %+v", book)
 		})
 
 		streambook := types.NewStreamBook(symbol)
 		streambook.BindStream(stream)
+		streambook.OnUpdate(func(book *types.OrderBook) {
+			bestBid, hasBid := book.BestBid()
+			bestAsk, hasAsk := book.BestAsk()
+
+			if !book.IsValid() {
+				log.Warnf("order book is invalid")
+				return
+			}
+
+			if hasBid && hasAsk {
+				log.Infof("================================")
+				log.Infof("best ask %f % -12f",
+					bestAsk.Price.Float64(),
+					bestAsk.Volume.Float64(),
+				)
+				log.Infof("best bid %f % -12f",
+					bestBid.Price.Float64(),
+					bestBid.Volume.Float64(),
+				)
+			}
+		})
 
 		log.Info("connecting websocket...")
 		if err := stream.Connect(ctx); err != nil {
diff --git a/pkg/exchange/binance/stream.go b/pkg/exchange/binance/stream.go
index b9eb94fd4..0ef5eaed3 100644
--- a/pkg/exchange/binance/stream.go
+++ b/pkg/exchange/binance/stream.go
@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"math/rand"
+	"os"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -16,9 +18,23 @@ import (
 	"github.com/c9s/bbgo/pkg/types"
 )
 
+var debugBinanceDepth bool
+
 func init() {
 	// randomize pulling
 	rand.Seed(time.Now().UnixNano())
+
+	if s := os.Getenv("BINANCE_DEBUG_DEPTH"); len(s) > 0 {
+		v, err := strconv.ParseBool(s)
+		if err != nil {
+			log.Error(err)
+		} else {
+			debugBinanceDepth = v
+			if debugBinanceDepth {
+				log.Info("binance depth debugging is enabled")
+			}
+		}
+	}
 }
 
 type StreamRequest struct {
@@ -457,21 +473,27 @@ func (f *DepthFrame) loadDepthSnapshot() {
 	}
 
 	f.mu.Lock()
+
+	// since we're buffering the update events, ideally the some of the head events
+	// should be older than the received depth snapshot.
+	// if the head event is newer than the depth we got,
+	// then there are something missed, we need to restart the process.
+	if len(f.BufEvents) > 0 {
+		e := f.BufEvents[0]
+		if e.FirstUpdateID > depth.FinalUpdateID+1 {
+			log.Warn("miss matched final update id for order book")
+			f.SnapshotDepth = nil
+			f.BufEvents = nil
+			f.mu.Unlock()
+			return
+		}
+	}
+
 	f.SnapshotDepth = depth
+	// filter the events by the event IDs
 
 	var events []DepthEvent
 	for _, e := range f.BufEvents {
-		/*
-			if i == 0 {
-				if e.FirstUpdateID > f.SnapshotDepth.FinalUpdateID+1 {
-					// FIXME: we missed some events
-					log.Warn("miss matched final update id for order book")
-					f.SnapshotDepth = nil
-					f.mu.Unlock()
-					return
-				}
-			}
-		*/
 		if e.FirstUpdateID <= f.SnapshotDepth.FinalUpdateID || e.FinalUpdateID <= f.SnapshotDepth.FinalUpdateID {
 			continue
 		}
@@ -490,10 +512,16 @@ func (f *DepthFrame) PushEvent(e DepthEvent) {
 		f.BufEvents = append(f.BufEvents, e)
 		f.mu.Unlock()
 
-		go f.once.Do(f.loadDepthSnapshot)
-		go func() {
+		go f.once.Do(func() {
+			if debugBinanceDepth {
+				log.Infof("starting depth snapshot updater for %s market", f.Symbol)
+			}
+
 			ctx := context.Background()
-			ticker := time.NewTicker(5*time.Minute + time.Duration(rand.Intn(10))*time.Second)
+
+			f.loadDepthSnapshot()
+
+			ticker := time.NewTicker(1*time.Minute + time.Duration(rand.Intn(10))*time.Second)
 			defer ticker.Stop()
 			for {
 				select {
@@ -503,7 +531,7 @@ func (f *DepthFrame) PushEvent(e DepthEvent) {
 					f.loadDepthSnapshot()
 				}
 			}
-		}()
+		})
 	} else {
 		if e.FirstUpdateID > f.SnapshotDepth.FinalUpdateID || e.FinalUpdateID > f.SnapshotDepth.FinalUpdateID {
 			if e.FinalUpdateID > f.SnapshotDepth.FinalUpdateID {
@@ -518,6 +546,10 @@ func (f *DepthFrame) PushEvent(e DepthEvent) {
 
 // fetch fetches the depth and convert to the depth event so that we can reuse the event structure to convert it to the global orderbook type
 func (f *DepthFrame) fetch(ctx context.Context) (*DepthEvent, error) {
+	if debugBinanceDepth {
+		log.Infof("fetching %s depth snapshot", f.Symbol)
+	}
+
 	response, err := f.client.NewDepthService().Symbol(f.Symbol).Do(ctx)
 	if err != nil {
 		return nil, err
diff --git a/pkg/types/orderbook.go b/pkg/types/orderbook.go
index 79c8a022d..66c1c05b9 100644
--- a/pkg/types/orderbook.go
+++ b/pkg/types/orderbook.go
@@ -123,6 +123,33 @@ type OrderBook struct {
 	asksChangeCallbacks []func(pvs PriceVolumeSlice)
 }
 
+func (b *OrderBook) BestBid() (PriceVolume, bool) {
+	if len(b.Bids) == 0 {
+		return PriceVolume{}, false
+	}
+
+	return b.Bids[0], true
+}
+
+func (b *OrderBook) BestAsk() (PriceVolume, bool) {
+	if len(b.Asks) == 0 {
+		return PriceVolume{}, false
+	}
+
+	return b.Asks[0], true
+}
+
+func (b *OrderBook) IsValid() bool {
+	bid, hasBid := b.BestBid()
+	ask, hasAsk := b.BestAsk()
+
+	if !hasBid || !hasAsk {
+		return false
+	}
+
+	return bid.Price < ask.Price
+}
+
 func (b *OrderBook) PriceVolumesBySide(side SideType) PriceVolumeSlice {
 	switch side {