Pool Replication Lag
Pool replication lag is the number of seconds that a Standby database or a read replica database lags behind the primary database.
This may be an indication that a transaction committed on the primary may not yet be committed on the downstream database.
This number should ideally always be 0; however, a non-zero value usually indicates some workload that is performing an excessive amount of inserts, updates, and deletes to the database, causing a delay in processing the transaction bin logs on the standby or read replica database.