In both examples 2 and 3, the author reads the same stream twice independently and assumes that a join is not synchronized between the transformed streams. This seems like a fundamental flaw in their offering.

Pushing in a timestamp along with the max/variance change stream[1]. And then using the timestamp to synchronize the join[2] would naturally produce a consistent output stream.

I quoted flink because they have the best docs around. But it should be possible in most streaming systems. Disclaimer, I used to work for the fb streaming group and have collaborated with the flink team very briefly.

[1] https://ci.apache.org/projects/flink/flink-docs-stable/dev/t...

[2] https://ci.apache.org/projects/flink/flink-docs-release-1.11...