[mmontagna9]

Sadly this isn't true. Postgres will happily replicate and skip data if you tell it too.

And there have been multiple bugs around logical replication in version ~10-15 that can cause data loss. None of these are directly related to lsn fiddling tho.

[AlisdairO]

Indeed - People In The Know have some cocnerns with this approach: https://ardentperf.com/2021/07/26/postgresql-logical-replica... .

At $work we did use this approach to upgrade a large, high throughput PG database, but to mitigate the risk we did a full checksum of the tables. This worked something like:

    * Set up logical replica, via 'instacart' approach
    * Attach physical replicas to the primary instance and the logical replica, wait for catchup
    * (very) briefly pause writes on the primary, and confirm catchup on the physical replicas
    * pause log replay on the physical replicas
    * resume writes on the primary
    * checksum the data in each physical replica, and compare

This approach required <1s write downtime on the primary for a very comprehensive data validation.