tornado + momoko 不处理连接

Question

我将 tornado (4.2.1) + momoko (2.2.0) + psycopg2 (2.6.1) 用于小型 Web 应用程序，它可以正常工作，直到 PostgreSQL 服务器关闭连接。然后在每个 db.execute() 命令之后，我都会收到一条错误消息：

Traceback (most recent call last):
      File "C:\Python27\lib\site-packages\tornado-4.2.1-py2.7-win32.egg\tornado\web.py", line 1415, in _execute
        result = yield result
      File "C:\Python27\lib\site-packages\tornado-4.2.1-py2.7-win32.egg\tornado\gen.py", line 870, in run
        value = future.result()
      File "C:\Python27\lib\site-packages\tornado-4.2.1-py2.7-win32.egg\tornado\concurrent.py", line 215, in result
        raise_exc_info(self._exc_info)
      File "C:\Python27\lib\site-packages\tornado-4.2.1-py2.7-win32.egg\tornado\gen.py", line 876, in run
        yielded = self.gen.throw(*exc_info)
      File "server.py", line 63, in get
        cursor = yield self.db.execute(query)
      File "C:\Python27\lib\site-packages\tornado-4.2.1-py2.7-win32.egg\tornado\gen.py", line 870, in run
        value = future.result()
      File "C:\Python27\lib\site-packages\tornado-4.2.1-py2.7-win32.egg\tornado\concurrent.py", line 215, in result
        raise_exc_info(self._exc_info)
      File "D:\work\program-stat\momoko\connection.py", line 453, in when_available
        future_or_result = method(conn, *args, **kwargs)
      File "D:\work\program-stat\momoko\connection.py", line 743, in execute
        cursor.execute(operation, parameters)
      File "C:\Python27\lib\site-packages\psycopg2\extras.py", line 288, in execute
        return super(NamedTupleCursor, self).execute(query, vars)
    OperationalError: server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.

这是一个代码：

import os
import tornado.httpserver
import tornado.ioloop
import tornado.options
import tornado.web
import momoko

from tornadotools.route import Route
from psycopg2.extras import NamedTupleCursor

import environments as env


tornado.options.define("port", default=9999, help="run on the given port", type=int)
tornado.options.define("pgsql_host", default=env.DB_HOST, help="database host")
tornado.options.define("pgsql_database", default=env.DB_DATABASE, help="database name")
tornado.options.define("pgsql_user", default=env.DB_LOGIN, help="database user")
tornado.options.define("pgsql_password", default=env.DB_PASSWORD, help="database password")


class Application(tornado.web.Application):
    def __init__(self):
        handlers = Route.routes()
        settings = dict(
            template_path=os.path.join(os.path.dirname(__file__), "templates"),
            static_path=os.path.join(os.path.dirname(__file__), "static"),
            debug=True,
        )
        tornado.web.Application.__init__(self, handlers, **settings)

        # Have one global connection to DB across all handlers
        self.db = momoko.Pool(
            dsn='dbname=%s user=%s password=%s '
                'host=%s port=5432' % (
                    tornado.options.options.pgsql_database,
                    tornado.options.options.pgsql_user,
                    tornado.options.options.pgsql_password,
                    tornado.options.options.pgsql_host),
            cursor_factory=NamedTupleCursor,
        )
        self.db.connect()


class BaseHandler(tornado.web.RequestHandler):
    @property
    def db(self):
        return self.application.db

@Route(r"/")
class HomeHandler(BaseHandler):
    def get(self):
        self.write("<ul>")
        self.write("<li><a href='/test'>Test page</a>")
        self.write("</ul>")
        self.finish()

@Route(r"/test")
class MogrifyHandler(BaseHandler):

    @tornado.web.asynchronous
    @tornado.gen.coroutine
    def get(self):
        cursor = yield self.db.execute("SELECT %s as t;", (1,))
        self.render("test.html", result=cursor.fetchall())


def main():
    tornado.options.parse_command_line()
    http_server = tornado.httpserver.HTTPServer(Application())
    http_server.listen(tornado.options.options.port)
    tornado.ioloop.IOLoop.instance().start()


if __name__ == "__main__":
    main()

如何处理此异常并自动重新连接到数据库而不重新启动应用程序？

Answer 1

龙卷风/桃子/自动重装

问题：

如果 Postgres 到数据库的连接被破坏 - momoko 无法重新创建连接池。 要解决此问题，您需要重新启动应用程序。为了使这个过程自动化，我编写了一个使用内置龙卷风更新机制的小脚本。

解决办法：

每隔 1 秒测试一次数据库连接是否有效。 在启动 ioloop 之前添加此检查。

导入重新加载 check_connect = tornado.ioloop.PeriodicCallback(lambda: reload.reload_if_db_pool_is_dead(application.db), 1000) check_connect.start()

https://gist.github.com/MaxRV/d7180e63d6b5396d904d446653aa7e88

Answer 2

你可以添加参数：

raise_connect_errors=False,

创建连接池时：

self.db = momoko.Pool(
    dsn='dbname=%s user=%s password=%s '
        'host=%s port=5432' % (
            tornado.options.options.pgsql_database,
            tornado.options.options.pgsql_user,
            tornado.options.options.pgsql_password,
            tornado.options.options.pgsql_host),
    cursor_factory=NamedTupleCursor,
    raise_connect_errors=False,
)

但这并不总是有用的。