Replication

A shopping cart write to cart-77 needs to land on enough replicas that a later read is guaranteed to see it — but "enough" is a number you choose, and the numbe…

A user changes their display name, refreshes the page a second later from a phone on a different network, and sees the old name. Nothing crashed. No request fai…

A team says "we need to shard the database" when the actual measured problem is a 200GB events table that scans slowly, or "let's add replication" when what the…