mongodb - 为什么 collection.InsertOne 在插入第一个元素时这么慢？

Question

我正在为 Go 测试新的官方 MongoDB 驱动程序，我注意到第一次调用 collection.InsertOne 总是花费大量时间，而所有后续调用都非常快。为什么？以及如何避免这种破坏性行为？

package main

import (
    "context"
    "log"
    "time"

    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
)

type Trainer struct {
    Name string
    Age  int
    City string
}

func main() {

    t1 := time.Now()

    // Set client options
    clientOptions := options.Client().ApplyURI("mongodb://localhost:27017")

    log.Println("Setting client options took", time.Now().Sub(t1))
    t1 = time.Now()

    // Connect to MongoDB
    client, err := mongo.Connect(context.TODO(), clientOptions)
    if err != nil {
        log.Fatal(err)
    }

    log.Println("Connecting took", time.Now().Sub(t1))
    t1 = time.Now()

    // Some dummy data to add to the Database
    ash := Trainer{"Ash", 30, "Pallet Town"}

    // Get a handle for your collection
    collection := client.Database("test").Collection("trainers")
    // Insert a single document

    log.Println("Getting the collection took", time.Now().Sub(t1))
    t1 = time.Now()

    for i := 0; i < 10; i++ {
        _, err := collection.InsertOne(context.TODO(), ash)
        if err != nil {
            log.Fatal(err)
        }
        log.Println("Inserting document took", time.Now().Sub(t1))
        t1 = time.Now()
    }

    err = client.Disconnect(context.TODO())

}

我预计所有插入操作都需要几毫秒或纳秒，而第一个大约需要 0.6 秒。这是带时间的日志:

2019/07/31 17:41:39 Setting client options took 0s
2019/07/31 17:41:39 Connecting took 0s
2019/07/31 17:41:39 Getting the collection took 0s
2019/07/31 17:41:40 Inserting document took 606.0339ms
2019/07/31 17:41:40 Inserting document took 0s
2019/07/31 17:41:40 Inserting document took 0s
2019/07/31 17:41:40 Inserting document took 0s
2019/07/31 17:41:40 Inserting document took 0s
2019/07/31 17:41:40 Inserting document took 0s
2019/07/31 17:41:40 Inserting document took 875.2µs
2019/07/31 17:41:40 Inserting document took 0s
2019/07/31 17:41:40 Inserting document took 0s
2019/07/31 17:41:40 Inserting document took 0s

Answer 1

只是为了结束评论中的问题:

MongoDB 驱动程序使用 lazy connection .查看MongoDB docs ，具体来说:

Calling Connect does not block for server discovery. If you wish to know if a MongoDB server has been found and connected to, use the Ping method:

ctx, _ = context.WithTimeout(context.Background(), 2*time.Second)
err = client.Ping(ctx, readpref.Primary())

这将强制连接并从您的第一个插入中删除插入延迟。