Out of curiosity: what are the scale limits of FoundationDB? What kind of issues would it start to have? For example, being able to store all of Discord messages on it?
I see blog posts of Discord moving to Scylla and ElasticSearch, but I wonder if there would be any difficulties here.
The one issue I remember is: On ES 5 we once had an issue early on where it regularly went down, turns out that some _very long_ input was being passed into the search by some scraper and killed the cluster.
The only bigger issue we had was when we initially added 10 nodes to double the initial capacity of the cluster. Performance tanked as a result, and it took us about half a day until we finally figured out that the new nodes were using dmraid (Linux RAID0) and as a result the block devices had a really high default read-ahead value (8192) compared to the existing nodes, which resulted in heavy read amplification. The ES manual specifically documents this, but since we hadn't run into this issue ourselves it took us a while to realise what was at fault.