asyncio service freezes for 600ms whenever a 5 MB upload arrives

The code that's running in prod

# ingest_api.py
# Receives JSON-LD documents, strips embedded scripts before parsing.

import json
import re
from aiohttp import web


async def parse_upload(request):
    body = await request.read()
    text = body.decode("utf-8")

    # Strip embedded <script> tags before JSON parsing.
    cleaned = re.sub(
        r"<script[^>]*>.*?</script>",
        "",
        text,
        flags=re.DOTALL | re.IGNORECASE,
    )
    parsed = json.loads(cleaned)

    return web.json_response({"ok": True, "fields": len(parsed)})

Log dashboard (last 60 seconds)

Pick the root cause

Four candidates. Three are plausible but mistake symptom for cause. Pick what you'd write in the postmortem timeline.