How to ensure replica is in sync between AWS RDS PSQL primary DB and Aurora RDS PSQL replica cluster?

Question

I am migrating RDS PSQL 11.13 to Aurora PSQL 11.13 provisioned DB instance as a part of that I have created read replica of Auroa PSQL but I couldn't confirm replica status. Replica lag metric in Aurora doesn't show any data?  where do I check to confirm sync is up-to-date ?

Answer

Please contact AWS Support in case you are not seeing replication lag in your CloudWatch metric. You can also use the query documented [here](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_PostgreSQL.Replication.ReadReplicas.html) to check replication lag.

"Check the amount of ReplicaLag between source DB instance and replicas. Replica lag is the amount of time, in milliseconds, that a read replica lags behind its source DB instance. This metric reports the result of the following query."

```
SELECT extract(epoch from now() - pg_last_xact_replay_timestamp()) AS replica_lag
```

How to ensure replica is in sync between AWS RDS PSQL primary DB and Aurora RDS PSQL replica cluster?

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