• asyncpg version: 0.20.1
• Cockroachdb version: v20.1.0 (connected to a 5-node on premise cluster)
• Python version: 3.8.0
• Platform: Linux
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes

Example code:

    async with pool.acquire() as conn:
        async with conn.transaction():
            if not await conn.table_exists("sys_app_config"):
                await conn.execute("""
                    CREATE TABLE sys_app_config(
                        key  text NOT NULL PRIMARY KEY,
                        value jsonb
                    );
                """)

The table_exists method looks like this:

class MyConnection(Connection):
    async def table_exists(self, table_name: str) -> bool:
        """Tell if a table exists."""
        return await self.fetchval(
            "select table_name from information_schema.tables where table_name=$1", table_name) is not None

This code is actually called from tornado.ioloop.IOLoop.current().run_sync so it is guaranteed that nothing else is running queries concurrently.

Here is the traceback that I'm getting:

 File "/home/user/my_project/db/initialize.py", line 19, in init_database
    if not await conn.table_exists("sys_app_config"):
  File "/home/user/.local/share/virtualenvs/backend-YgzYW8Ky/lib/python3.8/site-packages/asyncpg/transaction.py", line 91, in __aexit__
    await self.__commit()
  File "/home/user/.local/share/virtualenvs/backend-YgzYW8Ky/lib/python3.8/site-packages/asyncpg/transaction.py", line 179, in __commit
    await self._connection.execute(query)
  File "/home/user/.local/share/virtualenvs/backend-YgzYW8Ky/lib/python3.8/site-packages/asyncpg/connection.py", line 272, in execute
    return await self._protocol.query(query, timeout)
  File "asyncpg/protocol/protocol.pyx", line 316, in query
asyncpg.exceptions.FeatureNotSupportedError: unimplemented: multiple active portals not supported
HINT:  You have attempted to use a feature that is not yet implemented.
See: https://github.com/cockroachdb/cockroach/issues/40195

The referenced issue tells that it is not possible to keep multiple queries open and fetch from them interleaved.

However, I'm not doing anything that should result in opening multiple queries and fetching from them that way. As far as I see, my code should not open a new query before closing the previous one.

I suspect that asyncpg itself forgot to close something in the background.