PostgreSQL addon: optional logical replication for apps that need it

[LoudLemur]

Some apps now need PostgreSQL logical replication. The one I've hit is wger: since version 2.0, its mobile app requires PowerSync, which reads changes from the wger database through a logical replication slot. PowerSync, ElectricSQL, Supabase Realtime, Zero and Debezium all work this way.

The addon currently can't support this. The server runs with wal_level=replica, and app roles don't have the REPLICATION attribute. Neither can be changed from inside a package, so the only option is to bundle a separate PostgreSQL in the app and give up the addon's managed backups and upgrades.

Would you consider an opt-in addon option, something like "postgresql": { "logicalReplication": true }? It would need to:

• run the server with wal_level=logical (the only cost to other apps is somewhat more write-ahead log (WAL) volume)
• grant REPLICATION to the role of each app that asks for it
• set max_slot_wal_keep_size, so an abandoned slot can't fill the shared disk
• drop the app's replication slots on uninstall and before a restore

With that, packages like wger could stay on the addon instead of each shipping its own database.

[girish]

@loudlemur I will have to read up on this, to see what this is

[jdaviescoates]

@girish see also:

@roliG said:

FYI, it seems postgres 19 won't need the explicit "wal_level = replica", as it will automatically set it if there's a replication

[girish]

Oh thanks for that @jdaviescoates , i had missed that note from @rolig . So, we will roll out postgres 18 next week as part of 10.1. I guess we might just wait it out instead of adding this feature flag.

[jdaviescoates]

@girish said:

postgres 18

I presume you noticed, but, 18 is not 19

[roliG]

I presume you noticed, but, 18 is not 19

that's sadly true. 19 will be released... soon this autumn (also, I haven't tested that change yet, only have that from the docs)