>
> 1. what happens if an event arrives few days late? Looks like we have an
> unbound table with sorted time intervals as keys but I assume spark doesn't
> keep several days worth of data in memory but rather it would checkpoint
> parts of the unbound table to a storage at a specified interval
For watermarking you can read this excellent article: part 1:
https://www.oreilly.com/ideas/the-world-beyond-batch-streaming-101, part2:
https://www.oreilly.com/ideas/the-world-beyond-batch-streaming-102. It explains
more than just watermarking but it helped me understand a lot of the concepts
