psycopg2.ThreadConnectionPool,uWSGI和Flask的concurrrency问题

Question

我正在使用Flask,psycopg2和uWSGI.我psycopg2.ThreadConnectionPool用于数据库连接池,仅cursor.callproc用于查询数据库.

问题:有时,在并发请求期间,过程调用结果混淆,代码正在查询procedure_1但正在获得结果procedure_2(反之亦然,另一个并发客户端).即使uwsgi.ini存在threads=1,也只processes用于并发.maxconnfor psycopg2.ThreadConnectionPool设置为1.如果processes设置为1,则问题消失uwsgi.ini

什么可能导致问题？

以下是重现问题的简化代码:

烧瓶应用:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import contextlib

import flask
import psycopg2
import psycopg2.pool


app = flask.Flask(__name__)


class ThreadConnectionPool(psycopg2.pool.ThreadedConnectionPool):

    @contextlib.contextmanager
    def item(self):
    close = True
    connection = self.getconn()
    connection.autocommit = True
    try:
        yield connection
        close = False
    finally:
        self.putconn(connection, close=close or connection.closed)


pool = ThreadConnectionPool(maxconn=1, minconn=1, **kwargs)  # kwargs are omitted here 

# sp_1 always returns 1, sp_2 always returns 2
EXPECTED = {'sp_1': 1, 'sp_2': 2}


@app.route('/main/', methods=['GET'])
def main_handler():
    procname = flask.request.args['procname']

    with pool.item() as connection:
        cursor = connection.cursor()
        cursor.callproc(procname)

        rows = cursor.fetchall()

        if rows[0][0] == EXPECTED[procname]:
            return 'OK\n'
        else:
            # procedure returned something that it shouldn't return
            return 'ERROR\n'


if __name__ == '__main__':
    app.run()

uwsgi.ini:

[uwsgi]
callable=app
chdir=/path/to/my/project/
module=mymodule
master=True
processes=4 ; if 1, there is no problem
socket=127.0.0.1:9000
threads=1

程序:

-- sp_1
BEGIN
    Return 1;
END;


-- sp_2
BEGIN
    Return 2;
END;

再现(不是每次请求都会发生,而是经常发生):

curl 'http://mymodule.local/main/?procname=sp_1' & curl 'http://mymodule.local/main/?procname=sp_2'
[1] 10636
ERROR
ERROR
[1]+  Done                    curl 'http://mymodule.local/main/?procname=sp_1'

提前致谢!

Answer 1

您正在初始化主服务器中的线程池,在调用fork()(生成工作程序)之后,所有这些都将被搞砸(除非您管理它).确保为每个worker初始化池一次,或者在uWSGI中使用lazy-apps = true来为每个worker加载应用程序一次.