增加对数据库操作的统计命令：edge-node dbstat/减少几个不必要的查询操作

internal/utils/dbs/query_stat.go

@@ -0,0 +1,30 @@
+// Copyright 2022 Liuxiangchao iwind.liu@gmail.com. All rights reserved.
+
+package dbs
+
+type QueryStat struct {
+	Query   string
+	CostMin float64
+	CostMax float64
+
+	CostTotal float64
+	Calls     int64
+}
+
+func NewQueryStat(query string) *QueryStat {
+	return &QueryStat{
+		Query: query,
+	}
+}
+
+func (this *QueryStat) AddCost(cost float64) {
+	if this.CostMin == 0 || this.CostMin > cost {
+		this.CostMin = cost
+	}
+	if this.CostMax == 0 || this.CostMax < cost {
+		this.CostMax = cost
+	}
+
+	this.CostTotal += cost
+	this.Calls++
+}