[Snelius]

> Load in latest db dump, may take as long as it wants.

400TB its about a week+ ?

> Then start replication and catch up on the delay.

Then u have a changes in the delay about +- 1TB. It means a changes syncing about few days more while changes still coming.

They said "current requests are buffered" which is impossible, especial for long distributed (optional) transactions which in a progress (it can spend a hours, days (for analitycs)).

Overwall this article is a BS or some super custom case which irrelevant for common systems. You can't migrate w/o downtime, it's a physical impossible.

[freakynit]

Feels the same to me as well.

"Take snapshot and begin streaming replication"... like to where? The snapshot isn't even prepared fully yet and definitely hasn't reached the target. Where are you dumping/keeping those replication logs for the time being?

Secondly, how are you managing database state changes due to realtime update queries? They are definitely going in source table at this point.

I don't get this. Im still stuck on point 1... have read it twice already.

[mattlord]

It's open source. If you want to understand exactly how, you certainly can! :-)

https://github.com/vitessio/vitess

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

https://vitess.io/docs/reference/features/vtgate-buffering/

[Snelius]

He can't. It's not a reference, just a bunch of CLI examples. Please learn what is the reference. Even docs is a BS, wonderful product. Overall this article is a typical advertising and clickbait..

[joshuamorton]

The code is open source though, you can read it. The cli examples point you towards the relevant bits of the actual database code to read.

For my own sake, I'm not sure what is so surprising here. "Turn up a hot second replica and fail over to it intentionally behind a global load balancer." Is pretty well trodden ground.

[Snelius]

> The code is open source though, you can read it

Thank you! :D

> Is pretty well trodden ground.

YES!! But the article point us to it's a 400TB+ w/o downtime migration. This is impossible. That why is looks like clickbait and advertising of a product.

[joshuamorton]

I will simply point out that I'm aware of larger zero down-time migrations, like this one: https://www.youtube.com/watch?v=ih97gwNmkRA

[mattlord]

So you don't understand how something works. That's fine. But to then say the article and/or tech are BS is... a choice.

This work has been and is being used by some of the largest sites / apps in the world including Uber, Slack, GitHub, Square... But sure, "it's BS, super custom, and irrelevant". Gee, yer super smart! Thank you for the amazing insights. 5 stars.