Issues with async database queries in FastAPI causing unexpected delays
Quick question that's been bugging me - I'm attempting to set up I'm following best practices but I'm a bit lost with I'm encountering unexpected delays while executing asynchronous database queries in my FastAPI application using SQLAlchemy 1.4. The app seems to hang intermittently, particularly when multiple requests are processed simultaneously. I've implemented `async` and `await` correctly, but sometimes it takes several seconds to respond, even for simple queries. Here's a simplified version of my setup: ```python from fastapi import FastAPI, Depends from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker from sqlalchemy import Column, Integer, String, select DATABASE_URL = "postgresql+asyncpg://user:password@localhost/dbname" engine = create_async_engine(DATABASE_URL, echo=True) Base = declarative_base() class User(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) name = Column(String) async_session = sessionmaker(engine, class_=AsyncSession, expire_on_commit=False) app = FastAPI() async def get_db(): async with async_session() as session: yield session @app.get('/users/{user_id}') async def read_user(user_id: int, db: AsyncSession = Depends(get_db)): query = select(User).where(User.id == user_id) result = await db.execute(query) user = result.scalars().first() return user ``` When I run the app using `uvicorn main:app --host 0.0.0.0 --port 8000 --reload`, I notice that response times for the `/users/{user_id}` endpoint can vary greatly, particularly under load. I have tried using connection pooling settings by configuring `asyncpg` and altering the `max_overflow` option but with little effect. Also, I've tested the database separately and confirmed it's not the bottleneck. Any suggestions on diagnosing or optimizing this performance issue? Based on the logs, I sometimes see the following message, which might provide a clue: `asyncpg.exceptions.ConnectionDoesNotExistError: connection does not exist`. This error occurs sporadically and seems to correlate with the longer response times. I'm using FastAPI version 0.68.1 and SQLAlchemy version 1.4.27. Any insights would be greatly appreciated! I'm coming from a different tech stack and learning Python. The stack includes Python and several other technologies. This is my first time working with Python stable. How would you solve this? I'd really appreciate any guidance on this.