Here is a bizarre question that was asked on the Google office hours video asking if Google rotates its index. The question kind of makes sense, because the SEO who asked said on one day they see their page indexed, the next it is gone, then it comes back – is there an index rotation?
The answer is no, Google does not rotate its index.
Here was the question “Is it true that Google rotates indexed pages? Because the site I’m working on is rotating on indexed pages. Like for example, page A is indexed on Monday through Thursday, but not indexed Friday through Sunday.”
Lizzi from Google said “Okay. So the answer is real quick. No, this is not true. We are not rotating the index based off of days of the week.”
They don’t rotate the index based off of anything, even day of week actually.
This was asked at the 9:56 mark:
Forum discussion at Twitter.
