#34914: Postgres connection is not restarted after it's dropped by the server,
even
if we use CONN_HEALTH_CHECKS=True
-------------------------------------+-------------------------------------
Reporter: Vitor Menegat | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 4.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Simon Charette):
I think this is closely related to #32589 and #14845.
Django being mainly a web framework most of its connection management is
based around HTTP request lifecycle handling. For example, Django
automatically checks whether database connections should be closed
[https://github.com/django/django/blob/89d2ae257bfdbe6f32c4671d97bf572623992ace/django/db/__init__.py#L53-L61
when starting and finishing HTTP requests].
The way management commands were designed though didn't account for
lifecycle events for the framework to hook into and manage connections
appropriately. In other words, `BaseCommand.handle` is a blackbox to the
framework and it cannot safely determine that a unit of work is completed
and that is is safe to close a connection.
In the case of long-running / demonized commands that are meant to run for
longer than `CONN_MAX_AGE` (or the TTL of the underlying server
connection) it is the responsibility of the user to call
`close_old_connections`. This is something that is unfortunately not
documented but given how common this use case and the lack of progress on
#14845 in the past years I think we should consider a documentation
admonition that focuses solely on the long-runner command use case if that
means documenting this pattern more broadly.
If you feel so inclined to get this documented it appears to be a good
opportunity to resolve a 10 years old issue ;)
TL;DR the following should address your issue but it's unfortunately not
documented
{{{#!python
import logging
import time
from django.core.management import BaseCommand
from django.db import close_old_connections, connection
logger = logging.getLogger(__name__)
class Command(BaseCommand):
def handle(self, *args, **kwargs):
while True:
close_old_connections() # <- this ensures
DATABASES["default"]["CONN_*"] settings are honoured.
time.sleep(1)
try:
logger.info(f"health_check_enabled:
{connection.health_check_enabled}")
logger.info(f"health_check_done:
{connection.health_check_done}")
logger.info(f"errors_occurred:
{connection.errors_occurred}")
with connection.cursor() as cursor:
cursor.execute("SELECT 1")
logger.info("query executed")
except Exception as e:
logger.exception(e)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/34914#comment:3>
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