Comment by mattlord

It's open source. If you really want to know these things, I would encourage you to look at the code and read the documentation. As noted in the blog post, reverse vreplication is setup when you switch. You can switch back and forth and nothing is lost.

https://github.com/vitessio/vitess

https://vitess.io/docs/reference/vreplication/

"isn't this just pushing the same issue forward in time?" I don't understand what you are trying to say here. You can only compare the two sides / databases at the same logical point in time. While you are doing this comparison at that point in time, the timeline continues to progress. Unless you want to stop the world and prevent writes for the full duration of the diff (which can be days or even weeks).