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  1. Go Driver
  2. GODRIVER-1833

Connection pool `SetMaxPoolSize` not work in expected

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    • Type: Icon: Bug Bug
    • Resolution: Works as Designed
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: 1.4.4
    • Component/s: API
    • None
    • Environment:
      MongoDB == 2.6.12
      mongo-go-driver == 1.4.4

      First I run mongo 2.6.12 with docker:

      docker run -p 27018:27017 --name mongo26 -d mongo:2.6

      Then, I run this code to test connections, which set `SetMaxPoolSize(1)` to keep connection pool only one connection:

      package main

import (
    "context"
    "math/rand"
    "sync"
    "time"

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


func main() {
    opts := options.Client().
        ApplyURI("mongodb://127.0.0.1:27018").
        SetMaxPoolSize(uint64(1))
    client, err := mongo.NewClient(opts)
    if err != nil {
        panic(err)
    }

    if err := client.Connect(context.Background()); err != nil {
        panic(err)
    }

    var wg = &sync.WaitGroup{}
    for i := 0; i < 10; i++ {
        wg.Add(1)
        go queryData(client, wg)
    }
    wg.Wait()
}

func queryData(cli *mongo.Client, wg *sync.WaitGroup) {
    defer wg.Done()
    var coll = cli.Database("test").Collection("test")
    for i := 0; i < 1000000; i++ {
        coll.FindOne(context.Background(), bson.M{})
        time.Sleep(time.Nanosecond * time.Duration(rand.Intn(1000)))
    }
}

      While code is runing, check the connection between application and mongodb, there are 3 connections, which 2 greater than expected 1.

      ss -antp | grep 27018 | grep test
ESTAB      0      0               127.0.0.1:38932          127.0.0.1:27018 users:(("test",pid=764058,fd=7))    
ESTAB      0      0               127.0.0.1:38930          127.0.0.1:27018 users:(("test",pid=764058,fd=6))    
ESTAB      0      43              127.0.0.1:38938          127.0.0.1:27018 users:(("test",pid=764058,fd=8))

      Change the code to set connection pool size to 2 with :`SetMaxPoolSize(2)`，run the code again and check the connections：

      ss -antp | grep 27018 | grep test
ESTAB      0      0               127.0.0.1:38956          127.0.0.1:27018 users:(("test",pid=764331,fd=7))    
ESTAB      0      0               127.0.0.1:38954          127.0.0.1:27018 users:(("test",pid=764331,fd=6))    
ESTAB      0      43              127.0.0.1:38962          127.0.0.1:27018 users:(("test",pid=764331,fd=8))    
ESTAB      0      43              127.0.0.1:38966          127.0.0.1:27018 users:(("test",pid=764331,fd=9))

      It's 4, also 2 greater than expected 2.

            Assignee:
            isabella.siu@mongodb.com Isabella Siu (Inactive)
            Reporter:
            liqianglau@outlook.com Lau Liqiang
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            Watchers:
            3 Start watching this issue

              Created:
              Updated:
              Resolved: