A Single Redis Hot Key Can Defeat the Point of a Cluster
Redis Cluster spreads hash slots across shards, not one key across shards. A single extremely popular key can saturate the shard that owns it while the rest of the cluster is mostly idle.
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Redis Cluster Hash Tags Are a Data-Model Decision, Not a Syntax Trick
Hash tags let related keys share one slot so multi-key commands and scripts can remain atomic. Overuse them and you can create hot slots that undo the cluster's distribution.