Playgrounds

One concept per screen, fully interactive, free forever. No signup — break things and observe how systems fail under load.

Sharding & Hot Keys

Split a database across shards, skew the key distribution, and watch the hot shard melt. Then discover why adding shards doesn't save you.

Pick sync or async, set the lag, kill the primary — and count the writes you lost.

Tune the hit ratio and watch the origin eat the misses. Then flush the cache and meet the thundering herd.