Sharded counters

Count a thing that is incremented far faster than a single row, key, or partition can serialize writes — likes, views, votes, rate tallies, inventory decrements. The trap is the hot counter: every writer contends on one record, so latency climbs and throughput plateaus no matter how big the box is. Getting it wrong turns a trivial +1 into the bottleneck of the whole feature.

When to reach for this

Concurrent increments to a single logical count exceed what one row/key can absorb — a viral post's like count, a live-event view counter, a global rate tally. The symptom is write contention (lock waits, CAS retries, partition hot-spotting) on one record while the rest of the store is idle. Reaching for this means the write side is the problem, and an exact-to-the-millisecond total is not required.