gevent和posgres：異步連接失敗

Question

我正在使用gevent在基於Django的Web系統上處理API I/O。

我有猴子打補丁的使用：使用

import gevent.monkey; gevent.monkey.patch_socket() 

我修補psychopg：

import psycogreen; psycogreen.gevent.patch_psycopg() 

儘管如此，某些Django的調用等等Model.save（）與錯誤是失敗： 「異步連接失敗」。我是否需要在Django環境中做其他事情來使postgres成爲greenlet-safe？還有什麼我失蹤？

Answer 1

在這個問題上有一個article，不幸的是它是俄語。讓我引用最後一部分：

All the connections are stored in django.db.connections , which is the instance of django.db.utils.ConnectionHandler . Every time ORM is about to issue a query, it requests a DB connection by calling connections['default']. In turn, ConnectionHandler.__getattr__ checks if there is a connection in ConnectionHandler._connections , and creates a new one if it is empty.

All opened connections should be closed after use. There is a signal request_finished , which is run by django.http.HttpResponseBase.close . Django closes DB connections at the very last moment, when nobody could use it anymore - and it seems reasonable.

Yet there is tricky part about how ConnectionHandler stores DB connections. It uses threading.local , which becomes gevent.local.local after monkeypatching. Declared once, this structure works just as it was unique at every greenlet. Controller *some_view* started its work in one greenlet, and now we've got a connection in *ConnectionHandler._connections*. Then we create few more greenlets and which get an empty *ConnectionHandlers._connections*, and they've got connectinos from pool. After new greenlets done, the content of their local() is gone, and DB connections gone withe them without being returned to pool. At some moment, pool becomes empty

Developing Django+gevent you should always keep that in mind and close the DB connection by calling django.db.close_connection . It should be called at exception as well, you can use a decorator for that, something like:

class autoclose(object): 
    def __init__(self, f=None): 
     self.f = f 

    def __call__(self, *args, **kwargs): 
     with self: 
      return self.f(*args, **kwargs) 

    def __enter__(self): 
     pass 

    def __exit__(self, exc_type, exc_info, tb): 
     from django.db import close_connection 
     close_connection() 
     return exc_type is None