gevent e posgres: connessione asincrona fallita

Question

Sto usando gevent per gestire l'I/O API su un sistema web basato su Django.

ho scimmia-patched utilizzando: psychopg

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

ho patchato utilizzando:

import psycogreen; psycogreen.gevent.patch_psycopg() 

Ciò nonostante, certo Django chiama così Model.save() stanno fallendo con l'errore: "Connessione asincrona fallita." Devo fare qualcos'altro per rendere postgres greenlet-safe nell'ambiente Django? C'è qualcos'altro che mi manca?

Answer 1

c'è un article su questo promblem, sfortunatamente è in russo. Permettetemi di citare la parte finale:

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