I’ve been testing Go’s net package for managing 20,000 active connections. Initially, everything seems to work fine as memory usage stays around 150MB. However, when I disconnect all connections and try to reconnect them, the memory usage skyrockets to around 10GB and doesn’t seem to decrease.

Here’s a sample:

const (
    port       string = ":8080"
    maxClients uint64 = 20000
    bufSize           = 1024 * 1024 * 1 // 1MB buffer size

)

func handleConnection(conn net.Conn, wg *sync.WaitGroup) {
    defer wg.Done()
    defer conn.Close()

    buf := make([]byte, bufSize)
    for {
        n, err := conn.Read(buf)
        if err != nil {
            return
        }

        counter += 1
        bufferSize += int64(n)
        _, err = conn.Write(buf[:n])
        if err != nil {
            fmt.Println("Error writing:", err.Error())
            return
        }
    }
}

func main() {
    listener, err := net.Listen("tcp", port)
    if err != nil {
        fmt.Println("Error starting server:", err.Error())
        return
    }
    defer listener.Close()

    fmt.Println("Server started on port", port)

    var wg sync.WaitGroup
    sem := make(chan struct{}, maxClients)

    for {
        conn, err := listener.Accept()
        if err != nil {
            fmt.Println("Error accepting connection:", err.Error())
            continue
        }

        sem <- struct{}{}
        wg.Add(1)
        go func() {
            defer func() { <-sem }()
            handleConnection(conn, &wg)
        }()
    }

    wg.Wait()
}

I tried diffrent GOGC env value, didn’t help