Does Google Analytics have performance overhead?

Solution 1:

2018 update: Where and how you mount Analytics has changed over and over and over again. The current gtag.js code does a few things:

1. Load the gtag script but async (non-blocking). This means it doesn't slow your page down in any other way than bandwidth and processing.
2. Create an array on the page called window.datalayer
3. Define a little gtag() function that just pushes whatever you throw at it into that array.
4. Calls that with a pageload event.

Once the main gtag script loads, it syncs this array with Google and monitors it for changes. It's a good system and unlike the previous systems (eg stuffing code in just before </body>) it means you can call events before the DOM has rendered, and script order doesn't really matter, as long as you define gtag() first.

That's not to say there isn't a performance overhead here. We're still using bandwidth on loading up the script (it's cached locally for 15 minutes), and it's not a small pile of scripts that they throw at you, so there's some CPU time processing it.

But it's all negligible compared to (eg) modern frontend frameworks.

If you're going for the absolute, most cut-down website possible, avoid it completely. If you're trying to protect the privacy of your users, don't use any third party scripts... But if we're talking about an average modern website, there is much lower hanging fruit than gtag.js if you're hitting performance issues.

Solution 2:

There are some great slides by Steve Souders (client-side performance expert) about:

• Different techniques to load external JavaScript files in parallel
• their effect on loading time and page rendering
• what kind of "in progress" indicators the browser displays (e.g. 'loading' in the status bar, hourglass mouse cursor).

Solution 3:

I haven't done any fancy automated testing or programmatic number crunching, but using good old Firefox with the Firebug plugin and a pair of JS variables to tell the time difference before and after all GA code is executed, here is what I found.

Two things are downloaded:

1. ga.js is the JavaScript file containing the code. This is 9kb, so the initial download is negligible and the filename isn't dynamic so it's cached after the first request.

2. a 35 byte gif file with a dynamic url (via query string args), so this is requested every time. 35 bytes is a negligible download as well (firebug says it took me 70ms to dl it).

As far as execution time, my first request with a clean browser cache was an average of about 330ms each time and subsequent requests were between 35 and 130 ms.

Solution 4:

From my own experience it has adding Google-Analytics has not changed the load times.

According to FireBug it loads in less then a second (648MS avg), and according so some of my other test ~60% - 80% of that time was transferring the data from the server, which of course will vary from user to user.

I don't preticularly think that caching the analytics code locally will change the load times much, for the above reasons.

I use Google-Analytics on more then 40 websites without it ever being the cause of any, even small, slowdown, the most amount of time is spent getting the images which, due to their typical sizes, is understandable.