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)

Answer 1

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 2

There are two aspects to it.

1. Analytics script's' (and a gif) download
2. Downloaded scripts execution

Download time is almost always less than 100ms, which is acceptable.

Here comes the twist.

1. analytics.js execution 250ms
2. re-marketing (if enabled) 300ms
3. demographic (if enabled) 200ms

So analytics with re-marketing takes 750ms on average. I feel that this is a huge number when it comes to performance overhead.

Answer 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.

Answer 4

I noticed frequent I/o and CPU overload in cPanel resulting with:

Site unreachable error

And that stopped after I disabled WP Analytics plugin. So I reckon it does have some impact.