CDC: How to consistently ingest data from a changefeed

[lnhsingh]

Lauren Hirata Singh (lnhsingh) commented:

Include pseudocode algorithm for how to consistently ingest data from a changefeed with resolved timestamps (i.e. which messages to ignore based on their updated timestamp, which to upsert, how to know you've seen everything up to a given timestamp, etc.)

(Taken from #3992)

Jira Issue: DOC-260

[lnhsingh]

From #3992:

Dan: I gave an overview to roland once about how all these rules build up to some useful (and much easier to reason about) top-level invariants. We should document them at the top here and use that as context for all this stuff below. I'm happy letting this be a followup, just happened to think of it while reading the changes in this PR

Roland: I was just talking to Lauren offline about providing some pseudocode for "how to correctly consume a topic and interpret changefeed messages" - that might also be a good place to talk about the invariants?