django-db-geventpool

django-db-geventpool

Another DB pool using gevent for PostgreSQL DB.

psycopg3

Django, since 4.2, supports psycopg3. One of the advantages is that gevent is supported without needing extra patches, just install the package

$ pip install psycopg[binary]

psycopg2

If gevent is not installed, the pool will use eventlet as fallback.

• psycopg2>=2.5.1 for CPython 2 and 3 (or psycopg2-binary---see notes in the psycopg2 2.7.4 release)

• psycopg2cffi>=2.7 for PyPy

  Patch psycopg2

  Before using the pool, psycopg2 must be patched with psycogreen, if you are using gunicorn webserver, a good place is the post_fork() function at the config file:

  from psycogreen.gevent import patch_psycopg     # use this if you use gevent workers
  from psycogreen.eventlet import patch_psycopg   # use this if you use eventlet workers
  
  def post_fork(server, worker):
      patch_psycopg()
      worker.log.info("Made Psycopg2 Green")
  

Settings

• Set ENGINE in your database settings to:

    - For psycopg3: 'django_db_geventpool.backends.postgresql_psycopg3'
    - For psycopg2: 'django_db_geventpool.backends.postgresql_psycopg2'
    - For postgis: 'django_db_geventpool.backends.postgis'
  

• Add MAX_CONNS to OPTIONS to set the maximun number of connections allowed to database (default=4)

• Add REUSE_CONNS to OPTIONS to indicate how many of the MAX_CONNS should be reused by new requests. Will fallback to the same value as MAX_CONNS if not defined

• Add 'CONN_MAX_AGE': 0 to settings to disable default django persistent connection feature. And read below note if you are manually spawning greenlets

DATABASES = {
    'default': {
        'ENGINE': 'django_db_geventpool.backends.postgresql_psycopg',
        'NAME': 'db',
        'USER': 'postgres',
        'PASSWORD': 'postgres',
        'HOST': '',
        'PORT': '',
        'ATOMIC_REQUESTS': False,
        'CONN_MAX_AGE': 0,
        'OPTIONS': {
            'MAX_CONNS': 20,
            'REUSE_CONNS': 10
        }
    }
}

Using ORM when not serving requests

If you are using django with celery (or other), or have code that manually spawn greenlets it will not be sufficient to set CONN_MAX_AGE to 0. Django only checks for long-live connections when finishing a request - So if you manually spawn a greenlet (or task spawning one) its connections will not get cleaned up and will live until timeout. In production this can cause quite some open connections and while developing it can hamper your tests cases.

To solve it make sure that each greenlet function (or task) either sends the django.core.signals.request_finished signal or calls django.db.close_old_connections() right before it ends

The decorator method with your function is preferred, but the other alternatives are also valid

from django_db_geventpool.utils import close_connection

@close_connection
def foo_func()
     ...

or

from django.core.signals import request_finished

def foo_func():
   ...
   request_finished.send(sender="greenlet")

or

from django.db import close_old_connections

def foo_func():
   ...
   close_old_connections()

Other pools

• django-db-pool
• django-postgresql