Error 'Too Many Open Files' When Using SQLAlchemy with FastAPI and PostgreSQL
I'm currently using FastAPI with SQLAlchemy to connect to a PostgreSQL database, and I'm facing a 'Too Many Open Files' error intermittently when handling API requests. I've set up a basic application with a connection pool, but I suspect that my current configuration isn't properly managing database connections. I'm using SQLAlchemy 1.4.22 and FastAPI 0.68.0. Here’s a simplified version of my database connection setup: ```python from sqlalchemy import create_engine from sqlalchemy.orm import sessionmaker, scoped_session DATABASE_URL = "postgresql://user:password@localhost/dbname" engine = create_engine(DATABASE_URL, pool_size=10, max_overflow=20) session_factory = sessionmaker(bind=engine) session = scoped_session(session_factory) ``` In my FastAPI route, I am doing the following: ```python from fastapi import FastAPI, Depends app = FastAPI() @app.get("/items/{item_id}") async def read_item(item_id: int, db: Session = Depends(get_db)): result = db.query(Item).filter(Item.id == item_id).first() return result ``` I've tried adjusting the `pool_size` and `max_overflow` parameters, but I still encounter the error when multiple requests are made concurrently. The error message I get is: ``` sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) FATAL: remaining connection slots are reserved for non-replication superuser connections ``` I suspect that connections aren't being properly closed after requests are completed. I included a middleware to handle sessions, but the problem persists. Here's the middleware snippet: ```python from starlette.middleware.base import BaseHTTPMiddleware class DatabaseSessionMiddleware(BaseHTTPMiddleware): async def dispatch(self, request, call_next): response = await call_next(request) session.remove() # This should close the session return response ``` Can anyone provide insights on how to handle the connection pooling more effectively or identify what might be causing these connections to remain open? I'm looking for both code optimizations and best practices for managing database sessions in FastAPI with SQLAlchemy. Any help would be greatly appreciated!