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Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Unit and integration tests.

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.

1. Generate a correct producer snapshot prior to upload - this will be expensive because we either have to reply the log from the beginning or choose an arbitrary earlier segment as the starting point to start calculating said snapshot from.
2. Make Kafka wait to upload segments until it has expired all segments lacking a producer snapshot - we think this is just as counter-intuitive (especially if customers aren't well-aware of what producer snapshots are used for) and requiring niche knowledge as what the current approach is.
3. Do not allow a topic to have its tiering configuration set to true until all of its segments have an associated producer snapshot - the limitation here is that this condition needs to hold true across all brokers and additional synchronisation will be required.
4. Do not archive snapshot files - like indecies, snapshot files can be recreated by rereading the log. However, in the case of Tiered Storage we make the assumption that replaying the whole log will be quite costly.
5. Create empty snapshot files on read if a snapshot file is not found - this is a close second runner, but we chose to discard it. It would not be immediately obvious whether a snapshot is not presented because of an upgrade of Kafka version, because there is a bug in the plugin implementation or because the remote storage itself has been tampered with - if we explicitly write an empty file we reduce some of this ambiguity.