How to parse huge XML file with various elements in Go?

Use the standard xml Decoder.

Call Token to read tokens one by one. When a start element of interest is found, call DecodeElement to decode the element to a Go value.

Here's a sketch of how to use the decoder:

d := xml.NewDecoder(r)
for {
    t, tokenErr := d.Token()
    if tokenErr != nil {
        if tokenErr == io.EOF {
           break
        }
        // handle error
    }
    switch t := t.(type) {
    case xml.StartElement:
        if t.Name.Space == "foo" && t.Name.Local == "bar" {
            var b bar
            if err := d.DecodeElement(&b, &t); err != nil {
                // handle error
            }
            // do something with b
        }
    }
}