My company uses the same DB sharding tech. It took us about a year of daily / weekly outages until we finally were able to fix our performance issues. 256 database splits, lots of cross-shard queries removed, etc before we finally reached a happy-ish state for a year.

Now it’s scheduled to fall over in about 6 months and everyone is freaking out again. It’s not new features that are hurting us, it’s the existing core product line. All the new stuff is built on horizontally sharded DBs from the get-go.