110
hot key
One key gets a disproportionate share of traffic. The shard that owns it falls over. The others look idle.
What is hot key?
A hot key is a partition, cache entry, or row that attracts far more traffic than its neighbors. Celebrity accounts, a global counter, “latest” sorted by one timestamp. The node is busy. The cluster graph looks fine.
Why does hot key matter when vibe coding?
Models shard evenly on paper and store a single `stats:global` key. Launch day that key melts one node. Name the hot key before you pick the shard key.
How do you do hot key?
Find keys that are not uniform. Split them: per-shard counters you sum, or replicate a read-only copy. Do not hash a key everyone shares and expect balance.
How do you ask a model for hot key?
Assume (key) is hot. Do not put all of its traffic on one shard. Split counters or replicate the read. Do not use a single global key for a write on every request.
What goes wrong with hot key?
Adding shards without changing the key. The hot key still hashes to one of them. You bought nodes and kept the bruise.