What is the replication mode for Postgres Cloud SQL read replicas?

[Avishek Sen Gupta]

I think Google Groups ate up my first post, so here's another try:

For Postgres CloudSQL, can someone enlighten me as to how replication to Read Replicas is configured?

The documentation is pretty vague. It simply states: "A read replica is a copy of the master that reflects changes to the master instance in almost real time." The link is https://cloud.google.com/sql/docs/postgres/replication/create-replica

1) Is the replication mode cascading replication or streaming replication?

2) If it is streaming, is it asynchronous or synchronous?

3) If it is synchronous streaming, is it possible to know the value of the synchronous_commit flag? Is it off, local, on, remote_write, or remote_apply? This is as described here: https://www.postgresql.org/docs/11/warm-standby.html#STREAMING-REPLICATION

Thanks in advance!

[Manpreet Sidhu (Google Cloud Support)]

Postgres uses Write Ahead Logs for it’s replication. Based on the Postgres documentation that you provided, we notice that this method is Streaming Replication and is asynchronous. More details regarding Write Ahead Logs can be found on our community docs[1].

The value of the synchronus_commit flag is on, as is set by default[2].

I hope this helps.

[1]: https://cloud.google.com/community/tutorials/setting-up-postgres-hot-standby#understanding_hot_standby

[2]: https://www.postgresql.org/docs/11/runtime-config-wal.html