Python 烧瓶+SQLAlchemy操作错误

我正在尝试部署Flask应用程序。当我在Amazon的EC2上使用docker swarm运行代码时，我开始出现以下错误：

错误消息：

sqlalchemy.exc:OperationalError: (psycopg2.OperationalError) server closed the connection unexpectedly This probably means the server terminated abnormally before or while processing the request.[SQL: SELECT visitor."ID" AS "visitor_ID", visitor.username AS visitor_username, visitor.visits AS visitor_visits FROM visitor](Background on this error at: http://sqlalche.me/e/e3q8)

堆栈跟踪

Traceback (most recent call last):
File "/usr/local/bin/gunicorn", line 8, in <module>
File "/usr/local/lib/python3.7/site-packages/gunicorn/app/wsgiapp.py", line 58, in run
File "/usr/local/lib/python3.7/site-packages/gunicorn/app/base.py", line 228, in run
File "/usr/local/lib/python3.7/site-packages/gunicorn/app/base.py", line 72, in run
File "/usr/local/lib/python3.7/site-packages/gunicorn/arbiter.py", line 202, in run
File "/usr/local/lib/python3.7/site-packages/gunicorn/arbiter.py", line 545, in manage_workers
File "/usr/local/lib/python3.7/site-packages/gunicorn/arbiter.py", line 616, in spawn_workers
File "/usr/local/lib/python3.7/site-packages/gunicorn/arbiter.py", line 583, in spawn_worker
File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/base.py", line 140, in init_process
File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 123, in run
File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 67, in run_for_one
File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 29, in accept
File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 134, in handle
File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 175, in handle_request
File "/usr/local/lib/python3.7/site-packages/newrelic/api/wsgi_application.py", line 665, in _nr_wsgi_application_wrapper_
File "/usr/local/lib/python3.7/site-packages/newrelic/api/wsgi_application.py", line 193, in __init__
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 2463, in __call__
File "/usr/local/lib/python3.7/site-packages/newrelic/api/wsgi_application.py", line 555, in _nr_wsgi_application_wrapper_
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 2446, in wsgi_app
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1949, in full_dispatch_request
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1935, in dispatch_request
File "/usr/local/lib/python3.7/site-packages/newrelic/hooks/framework_flask.py", line 45, in _nr_wrapper_handler_
File "/app/src/views.py", line 5, in index
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3233, in all
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3389, in __iter__
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3414, in _execute_and_instances
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 982, in execute
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/sql/elements.py", line 293, in _execute_on_connection
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1101, in _execute_clauseelement
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1250, in _execute_context
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1476, in _handle_dbapi_exception
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 398, in raise_from_cause
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 152, in reraise
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1246, in _execute_context
File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/default.py", line 588, in do_execute
File "/usr/local/lib/python3.7/site-packages/newrelic/hooks/database_psycopg2.py", line 51, in execute
File "/usr/local/lib/python3.7/site-packages/newrelic/hooks/database_dbapi2.py", line 25, in execute

main.py文件：

import sys

from flask import Flask

from config import SQLALCHEMY_DATABASE_URI, HOST, PORT, DEBUG, DB_POOL_SIZE
from models import db


def make_app() -> Flask:
    flask_app = Flask(__name__)
    flask_app.config['SQLALCHEMY_DATABASE_URI'] = SQLALCHEMY_DATABASE_URI
    flask_app.config['SQLALCHEMY_POOL_SIZE'] = DB_POOL_SIZE
    add_urls(flask_app)
    db.init_app(app=flask_app)
    return flask_app


def add_urls(flask_app: Flask):
    from views import index, increment_visits
    flask_app.add_url_rule('/', view_func=index)
    flask_app.add_url_rule('/<username>/', view_func=increment_visits)


app = make_app()

if __name__ == '__main__':
    if 'createdb' in sys.argv:
        app.app_context().push()
        db.create_all()
    else:
        app.run(host=HOST, port=PORT, debug=DEBUG)

Docker服务：

ubuntu@srv1:~$ docker stack ps --filter "desired-state=running" demo
ID                  NAME                IMAGE                               NODE                DESIRED STATE       CURRENT STATE         ERROR               PORTS
frbdra27cdcb        demo_web.1          gonczor/aws-simple-app:prod         srv1                Running             Running 7 hours ago
0by6yhvr9n4a        demo_nginx.1        gonczor/aws-simple-app-nginx:prod   srv1                Running             Running 3 days ago
ym2t3we6r5b1        demo_db.1           postgres:11                         srv1                Running             Running 4 days ago
luwgpr3jnsj8        demo_web.2          gonczor/aws-simple-app:prod         srv1                Running             Running 7 hours ago

我不知道这个错误可能来自哪里，所以我很乐意提供任何进一步的细节

编辑

请求命令的输出：

simple_app=# SELECT sum(numbackends) FROM pg_stat_database;
 sum
-----
   2
(1 row)

---

我想我找到了一个解决办法，尽管我不清楚为什么它会起作用。我在中找到了答案，所以我们开始吧

该错误主要发生在长时间闲置之后。当我在基准测试期间向应用程序发送大量请求时，什么也没发生。似乎有些联系被SQLAlchemy保留了太长时间。我将池回收时间降低到10分钟，并更新了设置格式，以避免3.0版Flask SQLAlchemy中引入的弃用

DB_POOL_SIZE = int(os.environ.get('DB_POOL_SIZE', '10'))
DB_POOL_RECYCLE = int(os.environ.get('DB_POOL_RECYCLE', '60'))
SQLALCHEMY_ENGINE_OPTIONS = {
    'pool_size': DB_POOL_SIZE,
    'pool_recycle': DB_POOL_RECYCLE,
}

---

正如我所说，我不完全理解为什么这是一个问题，但在引入这些更改之后，没有出现任何错误。无论如何，欢迎评论和链接到解释此问题的资料。

实际的例外情况可能会有所帮助。您的模型是否设置为像Visitor.query一样使用。。。或者它们应该像db.session.queryVisitor一样使用…？是的，看起来回溯缺少实际的异常，最后一行被剪掉了？@djnzI我添加了实际的错误消息，models configuration。我尝试基于这些文档执行查询：PSQL可能会因为连接号过多而终止查询。请发布从pg_stat_数据库中选择sumnumbackends的结果。出于好奇，请在gunicorn_conf.py中更改为workers=1。

simple_app=# SELECT sum(numbackends) FROM pg_stat_database;
 sum
-----
   2
(1 row)

DB_POOL_SIZE = int(os.environ.get('DB_POOL_SIZE', '10'))
DB_POOL_RECYCLE = int(os.environ.get('DB_POOL_RECYCLE', '60'))
SQLALCHEMY_ENGINE_OPTIONS = {
    'pool_size': DB_POOL_SIZE,
    'pool_recycle': DB_POOL_RECYCLE,
}