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I mean to be fair, even in using something like Postgres logical replication, there's no way to verify whether a particular change has replicated (minus xmin hackery).

If I were to write a tutorial on how to set up PG replication and "observe the replication", I think that would probably involve "write to master, sleep for a bit, then see the data is in the secondary."

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The problem is that Postgres is a long lived server so the app can fire a commit to the DB and then exit. Here, the app needs to perform the sync, so you can't exit. I didn't see a way to confirm the sync was complete either, so when can you safely exit?

Couldn't you just query the replication log positions on the primary and standbys and calculate their delta?

I asked this to ChatGPT 4 and it suggested something like this that seems reasonable:

Get it from the main server: SELECT * FROM pg_stat_replication, and the write_ls column has the log transaction location; Then get the location of the replication log and how much has been received: SELECT pg_last_wal_receive_lsn(); Then you can figure out the delta from any of these: SELECT pg_wal_lsn_diff(write_ls, pg_last_wal_receive_lsn()); or similar.

That seems like it isn't a hack.

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