This document describes the current stable version of Celery (5.3). For development docs, go here.

Source code for celery.backends.database.session

"""SQLAlchemy session."""
import time

from kombu.utils.compat import register_after_fork
from sqlalchemy import create_engine
from sqlalchemy.exc import DatabaseError
from sqlalchemy.orm import sessionmaker
from sqlalchemy.pool import NullPool

from celery.utils.time import get_exponential_backoff_interval

try:
    from sqlalchemy.orm import declarative_base
except ImportError:
    # TODO: Remove this once we drop support for SQLAlchemy < 1.4.
    from sqlalchemy.ext.declarative import declarative_base

ResultModelBase = declarative_base()

__all__ = ('SessionManager',)

PREPARE_MODELS_MAX_RETRIES = 10


def _after_fork_cleanup_session(session):
    session._after_fork()


[docs]class SessionManager: """Manage SQLAlchemy sessions.""" def __init__(self): self._engines = {} self._sessions = {} self.forked = False self.prepared = False if register_after_fork is not None: register_after_fork(self, _after_fork_cleanup_session) def _after_fork(self): self.forked = True
[docs] def get_engine(self, dburi, **kwargs): if self.forked: try: return self._engines[dburi] except KeyError: engine = self._engines[dburi] = create_engine(dburi, **kwargs) return engine else: kwargs = {k: v for k, v in kwargs.items() if not k.startswith('pool')} return create_engine(dburi, poolclass=NullPool, **kwargs)
[docs] def create_session(self, dburi, short_lived_sessions=False, **kwargs): engine = self.get_engine(dburi, **kwargs) if self.forked: if short_lived_sessions or dburi not in self._sessions: self._sessions[dburi] = sessionmaker(bind=engine) return engine, self._sessions[dburi] return engine, sessionmaker(bind=engine)
[docs] def prepare_models(self, engine): if not self.prepared: # SQLAlchemy will check if the items exist before trying to # create them, which is a race condition. If it raises an error # in one iteration, the next may pass all the existence checks # and the call will succeed. retries = 0 while True: try: ResultModelBase.metadata.create_all(engine) except DatabaseError: if retries < PREPARE_MODELS_MAX_RETRIES: sleep_amount_ms = get_exponential_backoff_interval( 10, retries, 1000, True ) time.sleep(sleep_amount_ms / 1000) retries += 1 else: raise else: break self.prepared = True
[docs] def session_factory(self, dburi, **kwargs): engine, session = self.create_session(dburi, **kwargs) self.prepare_models(engine) return session()