#36957: Django psycopg connection pool + fork()
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Reporter: doc | Type: Bug
Status: new | Component: Uncategorized
Version: 6.0 | Severity: Normal
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Django's PostgreSQL backend stores psycopg_pool.ConnectionPool objects in
a class-level dict (DatabaseWrapper._connection_pools). When gunicorn (or
any pre-forking server) forks worker processes, all children inherit
references to the same pool objects — and crucially, the same underlying
TCP sockets to PostgreSQL. Multiple workers then read/write the same
socket concurrently, corrupting the PostgreSQL wire protocol.
**Root cause**
{{{
# django/db/backends/postgresql/base.py
class DatabaseWrapper(BaseDatabaseWrapper):
_connection_pools = {} # class-level dict — survives fork()
@property
def pool(self):
if self.alias not in self._connection_pools:
pool = ConnectionPool(...)
self._connection_pools.setdefault(self.alias, pool)
return self._connection_pools[self.alias]
}}}
**Workaround**
{{{
# gunicorn.conf.py
def post_fork(server, worker):
from django.db.backends.postgresql.base import DatabaseWrapper
DatabaseWrapper._connection_pools.clear()
}}}
**Suggested fix**
Use `os.register_at_fork(after_in_child=...)` to clear `_connection_pools`
in child processes, or check `os.getpid()` in the `pool` property and
recreate when it differs from the creating process.
**Tested with**
Django 6.0.2
psycopg 3.2.x – 3.3.2
psycopg-pool 3.2.x – 3.3.0
gunicorn 25.x (--worker-class asgi)
Python 3.12 – 3.14
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Ticket URL: <https://code.djangoproject.com/ticket/36957>
Django <https://code.djangoproject.com/>
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