Does Google Analytics have performance overhead?

Question

To what extent does Google Analytics impact performance?

I'm looking for the following:

• Benchmarks (including response times/pageload times et al)
• Links or results to similar benchmarks

One (possible) method of testing Google Analytics (GA) on your site:

1. Serve ga.js (the Google Analytics JavaScript file) from your own server.
2. Update from Google Daily (test 1) and Weekly (test 2).

I would be interested to see how this reduces the communication between the client webserver and the GA server.

Has anyone conducted any of these tests? If so, can you provide your results? If not, does anyone have a better method for testing the performance hit (or lack thereof) for using GA?

Answer 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.

Answer 2

Well, I have have searched, researched and expored extensively on net. But I have not found any statistical data that claims either in favour or against of the premise.

However, this excerpt from http://www.ga-experts.com claims that its a Myth that GA slows down your website.

Err, well okay, maybe slightly, but we’re talking about milliseconds. GA works by page tagging, and any time you add more content to a web page, it will increase loading times. However if you follow best practice (adding the tag before the </body> tag) then your page will load first. Also, bear in mind that any page tag based web analytics package (which is the majority) will work the same way

From the answers above and all other sources, what I feel is that whatever slowdown it causes in not percieved by the user as the Script is included at the bottom of the page. But if we talk of complete page-loads we might say that it slows down the page-load time.

Please post in more info if you have and DATA if you have any.

Answer 3

Nothing noticeable.

The call to Google (including DNS lookup, loading the Javascript if not already cached and the actual tracer calls themselves) should be done by the client's browser in a separate thread to actually loading your page. Certainly the DNS lookup will be done by the underlying system and will not, to my knowledge, count as a lookup within the browser (browsers have a limit on the number of request threads they will use per site).

Beyond that, the browser will load the Google script in parallel along with all other embedded resources, so you will potentially get an extremely slight increase in the time it takes to download everything, in the worst case (we're talking in the order of milliseconds, unnoticable. If the Google script is loaded last by the browser, or you don't have many external resources on your page, or if your page's external resources are cached by the browser, or if Google's script is cached by the browser (extremely likely) then you won't see any difference. It's just absolutely trivial overall, the same effect as sticking an extra tiny picture on your page, roughly speaking.

About the only time it might make a concrete difference is if you have some behaviour that fire on the onLoad event (which waits for external resources to load), and the Google servers are down/slow. The latter is unlikely to happen often, but if this were the case then the onLoad even won't fire until the script is downloaded. You can work around this anyway by using various "when DOM loaded" events, which are generally more responsive as you don't have to wait for your own scripts/images to load this way either.

If you're really that worried about the effects on page load time, then have a look a the "Net speed" section of Firebug, which will quantify this and draw you a pretty graph. I would encourage you to do this for yourself anyway as even if other people give you the figures and benchmarks you request, it will be completely different for your own site.

Answer 4

It really depends on the day. I'm just adding this to a blog. I'm in california, very close to their main data centers, on a fast low latency business DSL, on a overclocked i5 with plenty of RAM running a recent linux kernel and stable firefox.

here's a sample page load:

google-analytics alone added 5 seconds just of network download time... to get 15Kb!

You can see blogger.com served 34Kb in 300 mili seconds. That's 32x faster!

Also, look how the Red Line (which represents the onLoad event, meaning, there's no more script executing on the page and the so the browser can finally stops the loading indicators/spinings/etc) ... look how far to the right it is. that's probably 3seconds of garbage javascript processing that happened there. It's very uncommon for that line to be very far away from the end of the resources download bars. I'm done debugging this and it's 1/3 analytics fault, 2/3 blogger fault. ...one would think google stuff was fast.

Edit:

Some more data. Here's a request with everything cached. the above one was first visit.

I've removed the googleplus crap from above for two reasons, I was trying to see if they were playing some part on the slow onLoad event (they aren't) and because It is mostly useless.

So, With this we can see that the network time is the least of your worries. Even on a fast computer with modern software, the toll google analytics + blogger take on processing time will still dump your page load past 7s. Without the blogger, just check this very site, i'm seeing 0.5s of delay after resources are loaded and the red line kicks in.

Answer 5

There's no/minimal site overhead on the server side.

The HTML for Google Analytics is three lines of javascript that you place at the bottom of your webpage. It's nothing really, and doesn't consume any more server resource than a copyright notice.

On the client side, the page can take a little bit (up to a couple of seconds) of time to finish displaying a page. However - In my experience, the only bit of the page not loaded is the Google stuff, so users can see your page perfectly fine. You just get the throbber at the top of the page throbbing for a little longer.

(Note: You need to place your google analytics code block at the bottom of any served pages for this to be the case. I don't know what happens if the code block is placed at the top of your HTML)

Answer 6

The question was will Google Analytics cause your site to slow down and the answer is yes. Right now at the time of writing this Google-Analytics.com is not working so sites that have that in their pages won't load the pages so yes, it can slow down and cause your site to not even load. It's uncommon for google-analytics.com to be down this long which right now has been over 10 minutes, but it just shows that it is possible.