问题
So I just launched a website with Channels 2.0 Daphne 2.2.0 and asgi via Heroku (Hobby) and Postgres (trial). When I launch my website, I click around for a few pages and I get a 500 error. The error message I get emailed is FATAL: too many connections for role ..."
When I run heroku pg:killall or wait long enough I can click around a few more times until the error message repeats itself. However, when I run heroku pg it shows Connections 0/20. Does anyone know what is going on and how I can stop the errors? It's possible that I have two many connections open for a second, but it doesn't seem that way.
File "/app/.heroku/python/lib/python3.6/site-
packages/django/contrib/sessions/backends/base.py" in _get_session
191. return self._session_cache
During handling of the above exception ('SessionStore' object has no attribute '_session_cache'), another exception occurred:
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/base.py" in ensure_connection
216. self.connect()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/base.py" in connect
194. self.connection = self.get_new_connection(conn_params)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/postgresql/base.py" in get_new_connection
168. connection = Database.connect(**conn_params)
File "/app/.heroku/python/lib/python3.6/site-packages/psycopg2/__init__.py" in connect
130. conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
The above exception (FATAL: too many connections for role "polewdwynmvyyt"
) was the direct cause of the following exception:
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
35. response = get_response(request)
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
128. response = self.process_exception_by_middleware(e, request)
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
126. response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "./myproject/views.py" in home_page
8. print(request.session.get("first_name","Unknown")) #getter
File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in get
66. return self._session.get(key, default)
File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in _get_session
196. self._session_cache = self.load()
File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/db.py" in load
34. expire_date__gt=timezone.now()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/manager.py" in manager_method
82. return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in get
397. num = len(clone)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in __len__
254. self._fetch_all()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in _fetch_all
1179. self._result_cache = list(self._iterable_class(self))
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in __iter__
53. results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/sql/compiler.py" in execute_sql
1066. cursor = self.connection.cursor()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/base.py" in cursor
255. return self._cursor()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/base.py" in _cursor
232. self.ensure_connection()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/base.py" in ensure_connection
216. self.connect()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/utils.py" in __exit__
89. raise dj_exc_value.with_traceback(traceback) from exc_value
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/base.py" in ensure_connection
216. self.connect()
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/base.py" in connect
194. self.connection = self.get_new_connection(conn_params)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/postgresql/base.py" in get_new_connection
168. connection = Database.connect(**conn_params)
File "/app/.heroku/python/lib/python3.6/site-packages/psycopg2/__init__.py" in connect
130. conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
回答1:
Seems like the connections are not being reused and/or a new thread is being created for each request.
Remove the CONN_MAX_AGE from dj_database_url.config(default=DATABASE_URL) on settings.py (if you are using dj_database_url).
Set the environment variable ASGI_THREADS to a number of threads lower than your connections limit on your .asgi file or on heroku site -> settings -> configVars.
If you are using daphne, the default threads are CPU cores * 5, each thread with a connection.
example.asgi file:
import os
import django
from channels.routing import get_default_application
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "yourAppName.settings")
os.environ['ASGI_THREADS']="4"
django.setup()
application = get_default_application()
来源：https://stackoverflow.com/questions/51510259/django-heroku-fatal-too-many-connections-for-role