Database connection pool when using eventlet

django-database-connection-pool-eventlet.py

from django.core import signals
from django.db import connections
from django.db.utils import ConnectionHandler
from eventlet.pools import Pool

_unpatched_get_item = ConnectionHandler.__getitem__


class ConnectionPool(Pool):
    def __init__(self, alias, max_size=4):
        super().__init__(min_size=0, max_size=max_size, order_as_stack=False)
        self._alias = alias

    def create(self):
        conn = _unpatched_get_item(connections, self._alias)
        conn.inc_thread_sharing()
        return conn


def _patched_get_item(self, alias):
    # simple reuse within single request
    if hasattr(self._connections, alias):
        return getattr(self._connections, alias)

    # get a connection from the connection pool and bind it to the green thread
    if not hasattr(ConnectionHandler, 'connection_pool'):
        ConnectionHandler.connection_pool = {}

    if alias not in self.connection_pool:
        self.connection_pool[alias] = ConnectionPool(alias, max_size=4)

    conn = self.connection_pool[alias].get()
    conn.close_if_unusable_or_obsolete()
    setattr(self._connections, alias, conn)
    return conn


def put_connection_back_in_pool(sender, **kwargs):
    aliases = []
    for alias in connections:
        aliases.append(alias)
        conn = connections[alias]
        ConnectionHandler.connection_pool[alias].put(conn)

    for alias in aliases:
        del connections[alias]


def patch_connection_handler():
    signals.request_finished.connect(put_connection_back_in_pool)
    ConnectionHandler.__getitem__ = _patched_get_item