Database / ValKey Interview questions
Explain the execution flow of primary-replica replication in Valkey?
A replica initiates synchronization by sending PSYNC along with the replication ID and offset it last saw; the primary decides whether a partial or a full resynchronization is possible based on whether that offset is still covered by its backlog.
sequenceDiagram
participant R as Replica
participant P as Primary
R->>P: PSYNC replid offset
alt Offset in backlog
P->>R: +CONTINUE (partial resync)
else Offset too old
P->>R: +FULLRESYNC
P->>R: RDB snapshot transfer
end
P->>R: Stream of write commands
R->>P: REPLCONF ACK offset
For a full resync, the primary forks to stream an RDB snapshot (or streams it diskless, straight over the socket); once loaded, the replica keeps applying the live write stream from the backlog and periodically reports its progress back with REPLCONF ACK.
A replica reconnecting after a short disconnect first attempts...
Replicas report their replication progress back to the primary via...
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