I've used line-delimited, gzipped JSON for archive formats on several projects myself, which is a pretty good option... If I wanted more flexibility, would defi

I've used line-delimited, gzipped JSON for archive formats on several projects myself, which is a pretty good option... If I wanted more flexibility, would definitely consider SQLite. In fact, I've worked on several projects, where I heavily advocated that even the primary app storage was SQLite, and that archival was simply copying the database after an event. Specifically, elections, petition verification, etc. It's kind of difficult coming up with complex schemas to handle multiple events as well as the state of data at those events... by separating the database itself, using SQLite, that simplifies a lot of thigs. Though it does, practically limit scale a bit. The main thing would be to archive the application and the database after a given event. If the application is containerized, you could create an image of the source, the container and the database after the event. I think this kind of structure would work well for a lot of things... especially if you're considering data sharding anyway.