cache lowest/highest value (GET /info Only)

webapp/go/src/isucon8/isucoin/controller/handler.go

@@ -96,6 +96,7 @@ func (h *Handler) InternalInitialize(w http.ResponseWriter, r *http.Request, _ h
 	model.DemarkRunTrade()
 	model.InitTcMap(h.db)
 	model.InitUserCache()
+	model.InitCaches()
 
 	if err != nil {
 		h.handleError(w, err, 500)
@@ -270,24 +271,24 @@ func (h *Handler) Info(w http.ResponseWriter, r *http.Request, _ httprouter.Para
 		return
 	}
 
-	lowestSellOrder, err := model.GetLowestSellOrder(h.db)
+	lowestSellOrderPrice, err := model.GetLowestSellPriceOnly(h.db)
 	switch {
 	case err == sql.ErrNoRows:
 	case err != nil:
 		h.handleError(w, errors.Wrap(err, "model.GetLowestSellOrder"), 500)
 		return
 	default:
-		res["lowest_sell_price"] = lowestSellOrder.Price
+		res["lowest_sell_price"] = lowestSellOrderPrice
 	}
 
-	highestBuyOrder, err := model.GetHighestBuyOrder(h.db)
+	highestBuyOrderPrice, err := model.GetHighestBuyPriceOnly(h.db)
 	switch {
 	case err == sql.ErrNoRows:
 	case err != nil:
 		h.handleError(w, errors.Wrap(err, "model.GetHighestBuyOrder"), 500)
 		return
 	default:
-		res["highest_buy_price"] = highestBuyOrder.Price
+		res["highest_buy_price"] = highestBuyOrderPrice
 	}
 	// TODO: trueにするとシェアボタンが有効になるが、アクセスが増えてヤバイので一旦falseにしておく
 	res["enable_share"] = true

webapp/go/src/isucon8/isucoin/model/order.go

@@ -58,6 +58,55 @@ func getOrderByIDWithLock(tx *sql.Tx, id int64) (*Order, error) {
 	return scanOrder(tx.Query("SELECT * FROM orders WHERE id = ? FOR UPDATE", id))
 }
 
+type CachedInt64 struct {
+	lastUpdated time.Time
+	val         int64
+}
+
+var (
+	lowestPrice  CachedInt64
+	highestPrice CachedInt64
+)
+
+func InitCaches() {
+	lowestPrice.lastUpdated = time.Date(2000, 1, 1, 1, 1, 1, 0, time.Local)
+	highestPrice.lastUpdated = time.Date(2000, 1, 1, 1, 1, 1, 0, time.Local)
+}
+
+func GetLowestSellPriceOnly(d QueryExecutor) (int64, error) {
+	curTime := time.Now()
+	if lowestPrice.lastUpdated.Add(time.Millisecond * 300).After(curTime) {
+		return lowestPrice.val, nil
+	}
+
+	order, err := GetLowestSellOrder(d)
+	if err != nil {
+		return -1, nil
+	}
+
+	lowestPrice.lastUpdated = curTime
+	lowestPrice.val = order.Price
+
+	return lowestPrice.val, nil
+}
+
+func GetHighestBuyPriceOnly(d QueryExecutor) (int64, error) {
+	curTime := time.Now()
+	if highestPrice.lastUpdated.Add(time.Millisecond * 300).After(curTime) {
+		return highestPrice.val, nil
+	}
+
+	order, err := GetHighestBuyOrder(d)
+	if err != nil {
+		return -1, nil
+	}
+
+	highestPrice.lastUpdated = curTime
+	highestPrice.val = order.Price
+
+	return highestPrice.val, nil
+}
+
 func GetLowestSellOrder(d QueryExecutor) (*Order, error) {
 	return scanOrder(d.Query("SELECT * FROM orders WHERE type = ? AND closed_at IS NULL ORDER BY price ASC, created_at ASC LIMIT 1", OrderTypeSell))
 }

webapp/go/src/isucon8/isucoin/webapp/main.go

@@ -62,6 +62,7 @@ func main() {
 	h := controller.NewHandler(db, store)
 	model.InitTcMap(db)
 	model.StartRunTradeGoRoutine(db)
+	model.InitCaches()
 
 	router := httprouter.New()
 	router.POST("/initialize", h.Initialize)