Last post before we went down (2022-07-08 12:46:04 UTC): https://news.ycombinator.com/item?id=32026565
First post once we were back up (2022-07-08 20:30:55 UTC): https://news.ycombinator.com/item?id=32026571 (hey, that's this thread! how'd you do that, tpmx?)
So, 7h 45m of downtime. What we don't know is how many posts (or votes, etc.) happened after our last backup, and were therefore lost. The latest vote we have was at 2022-07-08 12:46:05 UTC, which is about the same as the last post.
There can't be many lost posts or votes, though, because I checked HN Search (https://hn.algolia.com/) just before we brought HN back up, and their most recent comment and story were behind ours. That means our last backup on the ill-fated server was taken after the last API update (HN Search relies on our API), and the API gets updated every 30 seconds.
I'm not saying that's a rock-solid argument, but it suggests that 30 seconds is an upper bound on how much data we lost.
Is your backup system tied to your API? Algolia is a third party service, and streaming the latest HN data to Algolia seems pretty similar to streaming it to a backup system.