Google’s John Mueller recently provided advice to site owners regarding A/B testing during a site migration.
According to Mueller, conducting an A/B test during a site migration can cause the process to take significantly longer than it needs to.
This was a topic that came up in a Google Webmaster Central hangout when someone asked the following question:
“What would be the impact if an A/B test is running while a large-scale URL migration launches? All old URLs properly 301 redirect to new URLs, but Googlebot is sometimes redirected to test URLs while the migration goes live… could this impact how signals are passed and potentially lengthen the time a site sees of volatility?”
Mueller had a lot to say in response to this question, providing a much longer answer than he usually does in these hangouts.
It’s best to refrain from conducting large sets of A/B tests during a site migration, Mueller says.
During a site migration Google will try to understand what the general picture is with a website.
The better Google can understand what’s going on with a site, the easier it will be to move all algorithmic signals from the old site to the new site.
If there’s a “fancy” A/B test going on during a site migration then it will take longer for Google to understand what’s happening.
Mueller strongly advises site owners to provide as clean a signal as possible during a site migration.
In particular, he recommends checking for the following things:
Make sure that all the URLs from the old site are redirecting to the new version.
Make sure there are no crawl errors from URLs that should be available.
Don’t have anything blocked by robots.txt that wasn’t blocked by robots.txt before.
This will all help provide the signals that Google needs to efficiently process a site migration.
Once again — give a clean signal that you’re doing a straightforward move from one version of a site to another. Otherwise it will take a lot longer to process.
You can see Mueller’s full response in the video below, starting at the 11:17 mark.
“I don’t know if this would cause big issues in the bigger picture. Usually when you’re doing A/B testing it’s a small group of URLs within a website, it’s not that all URLs of your website are doing this A/B testing thing where sometimes we see one URL and sometimes we get redirected to another one.
For small sets of URLs I don’t see the problem there. For bigger sets of A/B tests I would try to minimize this as much as possible. The reason being is that, especially for site migrations, when you’re moving to a different domain, when you’re changing within the same domain, when you’re changing to HTTPS, with these things we try to understand what the general picture is with the website.
Is the website moving from one domain to another? Is the website moving to HTTPS, for example. And the clearer we can get a picture of what is actually happening here, the clearer we can apply kind of an algorithm to move all of the signals we have from this website to the new version of that website.
So if during a site migration you’re doing some kind of fancy A/B testing, and sometimes we see redirects to one direction, and sometimes we see site migration redirects, then that can certainly throw us off in the bigger picture and can delay the overall move from one version to another.
So especially when it comes to site migrations, the cleaner you can set that up the more you can make sure that all the URLs are redirecting to the new version, that you don’t have crawl errors from URLs which should be available, that you don’t have things blocked by robots.txt that weren’t blocked by robots.txt before, all of these things.
The cleaner you can get the more likely we’ll be able to say “oh, this is obviously a move from here to here, therefore we don’t even need to worry about all of the details we can just shuffle everything over.”
Whereas if we look at it and we say “well, maybe it’s a move, or maybe they’re doing something fancy, maybe we should take a bit more time to figure out what exactly is happening here.” That can end up causing a site migration to take significantly longer than it really needs to take.”