gevent und posgres: Asynchrone Verbindung fehlgeschlagen

Question

Ich benutze Gevent, um API I/O auf einem Django-basierten Web-System zu behandeln.

Ich habe affen gepatcht mit:

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

Ich habe gepatcht psychopg mit:

import psycogreen; psycogreen.gevent.patch_psycopg() 

Dennoch bestimmte Django nennt so Model.save() mit dem Fehler Fehler: "Asynchrone Verbindung fehlgeschlagen." Muss ich etwas anderes tun, um Postgres-Greenlet-sicher in der Django-Umgebung zu machen? Gibt es noch etwas, das mir fehlt?

Answer 1

gibt es eine article auf diesem Problem, leider ist es in russischer Sprache. Lassen Sie mich den letzten Teil zitieren:

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