No objects ever released by the GC, potential memory leak?

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn’t find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google “How to X in FastAPI” and didn’t find any information.
• I already read and followed all the tutorial in the docs and didn’t find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

# From the official documentation
# Run with uvicorn main:app --reload
from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def root():
    return {"message": "Hello World"}

Description

Use the minimal example provided in the documentation, call the API 1M times. You will see that the memory usage piles up and up but never goes down. The GC can’t free any objects. It’s very noticeable once you have a real use case like a file upload that DoS’es your service.

Here some examples from a real service in k8s via lens metrics:

Operating System

Linux, macOS

Operating System Details

No response

FastAPI Version

0.74.1

Python Version

Python 3.10.1

Additional Context

No response

[darkclouder]

The memory leak in uvicorn is probably not the cause of my issue though. First of all, it only happens with FastAPI >=0.69.0, and I also had apps where that happens where I don’t even use app.state or request.state at all. I think I will put some more effort in isolating a minimal running version with that memory leak for my case. I’ll get back to you if I manage to do that.

[Kludex]

I can reproduce it on Python 3.7.13, but it’s not reproducible from 3.8+.

Notes:

• This issue can be reproduced with pure Starlettte - this means this issue can be closed here.
• This issue cannot be reproduced on Python 3.8+.
• This issue cannot be reproduced with Starlette 0.14.2 (version pre-anyio) in Python 3.7.
• This issue can only be reproduced by Starlette 0.15.0+ on Python 3.7.

I’ll not spend more time on this issue. My recommendation is to bump your Python version.

In any case, this issue doesn’t belong to FastAPI.