Replication, Sentinel and Cluster in Redis: Failover, Hash Slots, Hash Tags and CROSSSLOT
Because Redis replication is asynchronous, a write acknowledged to the client can be lost in a failover; WAIT does not prevent this, it only makes it visible. With real output: a lost order number, failover time with Sentinel and StackExchange.Redis, 16384 hash slots in Cluster, MOVED, CROSSSLOT and hash tags, Functions that must be loaded on every primary, node-local keyspace notifications, Redis 8.4's atomic slot migration and how Valkey 9 differs.
14 Nov 2026
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12 min
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