Using statement_cache_size asyncpg setting / prepared statement name for asyncpg w pgbouncer

Hi!

I use sqlalchemy 1.4 with asyncpg driver with pgbouncer.

    from sqlalchemy.ext.asyncio import create_async_engine
    from sqlalchemy.orm import sessionmaker
    from sqlalchemy.ext.asyncio import AsyncSession

    engine = create_async_engine(
        f'postgresql+asyncpg://{username}:{password}@{host}:{port}/{dbname}',
        echo=False,
    )
    session_maker = sessionmaker(
        engine,
        class_=AsyncSession,
    )

I have an error:

asyncpg.exceptions.DuplicatePreparedStatementError: prepared statement "__asyncpg_stmt_a__" already exists
HINT:
NOTE: pgbouncer with pool_mode set to "transaction" or
"statement" does not support prepared statements properly.
You have two options:

* if you are using pgbouncer for connection pooling to a
  single server, switch to the connection pool functionality
  provided by asyncpg, it is a much better option for this
  purpose;

* if you have no option of avoiding the use of pgbouncer,
  then you can set statement_cache_size to 0 when creating
  the asyncpg connection object.

How i can pass this setting (statement_cache_size=0) to asyncpg connection object?

[jacksund]

I do have a working setup in transaction mode using https://github.com/sqlalchemy/sqlalchemy/issues/6467#issuecomment-864943824 though:

from uuid import uuid4
from asyncpg import Connection

class CConnection(Connection):
    def _get_unique_id(self, prefix: str) -> str:
        return f"__asyncpg_{prefix}_{uuid4()}__"

engine = create_async_engine(
    "postgresql+asyncpg://scott:tiger@localhost/test",
    echo=True,
    connect_args={
        "statement_cache_size": 0,
        "prepared_statement_cache_size": 0,
        "connection_class": CConnection,
    },
)

[SlavaSkvortsov]

We had a similar problem due to multiple web workers. They generated prepared statements with the same names - original function to generate IDs looks like this:

    def _get_unique_id(self, prefix):
        global _uid
        _uid += 1
        return '__asyncpg_{}_{:x}__'.format(prefix, _uid)

So we just changed the Connection class a bit

from uuid import uuid4

from asyncpg import Connection


class CConnection(Connection):
    def _get_unique_id(self, prefix: str) -> str:
        return f'__asyncpg_{prefix}_{uuid4()}__'

You need to provide it when you create the engine

engine = create_async_engine(
    settings.database_url,
    connect_args={
        'connection_class': CConnection,
    },
)