Comparison
Ingestion lagvsReplication lag
Ingestion lag
the row was committed in the source at 09:00 and appeared in the warehouse at 09:41, and nobody could say which hop ate the forty minutes.
The delay between a change happening in the source and it being queryable at the destination. It is the number the business actually feels, and it is a sum over every hop, so it can only be diagnosed if each stage stamps its own arrival time. Measuring it end to end rather than per component is the difference between 'the pipeline is slow' and 'the connector is fine, the merge step waits for a lock'.
Full entry →Replication lag
the replica is forty seconds behind the primary and the report you generated from it is missing this morning's orders.
How far behind a follower is from the leader, measured in time or log position. It grows under write bursts, long transactions, and single-threaded replication apply. It is the number to alert on before you send any read traffic to replicas, and the number that decides whether a failover loses data.
Full entry →