6.3 Replication and Read Replicas

127.0.0.1:6379> SET order:981 paid
OK
127.0.0.1:6379> WAIT 1 100
(integer) 0

The primary replied OK to the SET at once, yet 100 milliseconds later WAIT reports that no replica has confirmed the write, because both replicas were lagging at that moment. Both replies are normal behavior. Replication in Redis is asynchronous: the primary acknowledges a write as soon as it executes it locally, and replicas receive the change a moment later. That gap decides what a read replica may return, what a failover may lose, and what WAIT can and cannot promise.