Feature request: 'get_attributes' without prepared statements

Hello!

Right now I’m trying out the AsyncSession in the SQLAlchemy@1.4 which uses asyncpg under the hood and as it turns out that specific configuration does not work well with pgbouncer even if you disable statement caching both in asyncpg and SQLAlchemy.

As discussed in the corresponding issue — https://github.com/sqlalchemy/sqlalchemy/issues/6467 — SQLAlchemy uses Connection.prepare() regardless of user’s decision on whether or not to use prepared statements. It is required to fetch the query attributes.

It looks like if there would be an ability to fetch attributes of the query without preparing it first, the issue could be mitigated. Therefore, I wanted to ask if there is a way to fetch those attributes without calling Connection.prepare() first?

cc @zzzeek

[elprans]

I wanted to ask if there is a way to fetch those attributes without calling Connection.prepare() first?

Alas, no. Asyncpg is fundamentally built around the Postgres extended query protocol, and so the API and the implementation are built around that. The other way to get information about the query result is to run it with the simple query protocol, but we can’t use that, because the protocol does not return enough information about the attribute types to decode them effectively and so we must introspect the type catalog to build the decoding pipeline.

Looking at https://github.com/sqlalchemy/sqlalchemy/issues/6467, it seems like the issue isn’t necessarily that prepare() doesn’t work, it’s that prepared statement names aren’t unique across connections and pgbouncer mixes them up. Merging #775 might help with this, although I need to think whether that should be unconditional or based on some connection parameter, since UUID generation isn’t necessarily very fast.

[elprans]

Yeah, I think so.