It takes too much time when using "template" package to generate a dynamic web page to client in Golang

Question

It is so slow when using template package to generate a dynamic web page to client.

Testing code as below, golang 1.4.1

http.Handle("/js/", (http.FileServer(http.Dir(webpath))))
http.Handle("/css/", (http.FileServer(http.Dir(webpath))))
http.Handle("/img/", (http.FileServer(http.Dir(webpath))))
http.HandleFunc("/test", TestHandler)


func TestHandler(w http.ResponseWriter, r *http.Request) {

    Log.Info("Entering TestHandler ...")
    r.ParseForm()

    filename := NiConfig.webpath + "/test.html"

    t, err := template.ParseFiles(filename)
    if err != nil {
        Log.Error("template.ParseFiles err = %v", err)
    } 

    t.Execute(w, nil)
}

According to the log, I found that it took about 3 seconds in t.Execute(w, nil), I do not know why it uses so much time. I also tried Apache server to test test.html, it responded very fast.

Answer 1

You should not parse templates every time you serve a request!

There is a significant time delay to read a file, parse its content and build the template. Also since templates do not change (varying parts should be parameters!) you only have to read and parse a template once.
Also parsing and creating the template each time when serving a request generates lots of values in memory which are then thrown away (because they are not reused) giving additional work for the garbage collector.

Parse the templates when your application starts, store it in a variable, and you only have to execute the template when a request comes in. For example:

var t *template.Template

func init() {
    filename := NiConfig.webpath + "/test.html"
    t = template.Must(template.ParseFiles(filename))

    http.HandleFunc("/test", TestHandler)
}

func TestHandler(w http.ResponseWriter, r *http.Request) {
    Log.Info("Entering TestHandler ...")
    // Template is ready, just Execute it
    if err := t.Execute(w, nil); err != nil {
        log.Printf("Failed to execute template: %v", err)
    }
}