from asyncache import cached
from cachetools import TTLCache

pool = ...

@cached(TTLCache(1024, 60))
async def get_username(user_id):
    rec = await pool.fetchrow(
        """
        SELECT
            username
        FROM
            users
        WHERE
            id = $1
        """,
        user_id,
    )
    return rec and rec["username"]