support read replicas config

[steebchen]

No description provided.

[nettrino]

@steebchen even without this being implemented yet, is it possible to have NewClient accept a URL and thus to have two clients active, one for the read replica and one for the write replica just by means of passing different URLs?

[steebchen]

I haven't tried it but it might work yeah @nettrino

[nettrino]

I think client := db.NewClient(db.WithDatasourceURL(url)) might not be properly overwriting the URL if we have a single schema with a single datasource, however I will need to double check and come back to this ticket.

Update: locally, if I have a schema with a datasource

datasource db {
    provider = "postgresql"
    url      = env("DATABASE_URL")
    schemas  = ["public", "backend"]
}

with DATABASE_URL being set to postgresql://postgres:postgres@localhost:5432/postgres?application_name=foo
and I initiate two clients within my server, one with db.NewClient() and the other client with client := db.NewClient(db.WithDatasourceURL(url)) with url being postgresql://postgres:postgres@localhost:5432/postgres?application_name=bar while the first client is also running, only one of the two shows up in the DB if I run

SELECT DISTINCT application_name
FROM pg_stat_activity
WHERE application_name IS NOT NULL;

and spin up my server - so I think this might be a bug @steebchen ?

[steebchen]

What happens when you initiate both with WithDatasourceURL and not set an env var outside of your application? Maybe it's overwriting it.

[nettrino]

I don't think this is doable to not set an env var at all - if I use an empty URL I get

"msg":"Error connecting prisma","error":"spawn: query engine errored: Error in data model: Diagnostics { errors: [DatamodelError { span: Span { start: 1125, end: 1127, file_id: FileId(0) }, message: \"Error validating datasource `db`: You must provide a nonempty URL\" }], warnings: [] }"}

If I do set the env var and simply initialize both with WithDatasourceURL it does not seem to work either

[nettrino]

@steebchen did you manage to replicate the above by any chance?