Django/Heroku：致命：角色的连接太多

所以我刚刚通过 Heroku（业余爱好）和 Postgres（试用版）推出了一个包含 Channels 2.0 Daphne 2.2.0 和 asgi 的网站。当我启动网站时，我点击了几个页面，然后收到 500 错误。我通过电子邮件收到的错误消息是FATAL: too many connections for role ..."

当我跑步时heroku pg:killall或者等待足够长的时间，我可以再单击几次，直到错误消息重复出现。然而，当我跑步时heroku pg表明Connections 0/20。有谁知道发生了什么事以及我如何阻止错误？我可能有两个连接打开了一秒钟，但看起来并非如此。

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)

似乎连接没有被重用和/或正在为每个请求创建一个新线程。

去除CONN_MAX_AGE from dj_database_url.config(default=DATABASE_URL) on settings.py（如果您使用的是 dj_database_url）。

设置环境变量ASGI_THREADS线程数低于您的连接限制.asgi文件或在 heroku 站点 -> 设置 -> configVars. 如果使用daphne，默认线程是CPU核心*5，每个线程有一个连接。

示例.asgi 文件：

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()