Hello.
We run our web application in cherrypy. I have just found that all our threads
share *one* DB connection! A web page contains several AJAX calls, each queries
the database. However only one runs at a time because the threads share DB
connection.
Notes to the code below:
* We run postgres 9.1 via psycopg2.
* db.init() creates engine with pool_size of 5 by default.
* scoped_session() ensures that each thread gets its own session object.
* See our module session and its use.
I have no idea what is wrong. Please help me diagnose this! Note that OS monitor
shows several cherrypy threads, each gets its share, so the cherrypy setup seems
to be OK.
Thank you in advance,
Ladislav Lenart
####################
# Snippet of db.py #
####################
def init(conn_string, echo=False, base=None, pool_size=5):
engine = create_engine(conn_string, echo=echo, pool_size=pool_size)
session.init(engine)
if base is None:
base = Base
_import_model()
base.metadata.bind = engine
return engine
#########################
# Snippet of session.py #
#########################
_Session = None
def init(engine):
global _Session
_Session = scoped_session(sessionmaker(bind=engine, autoflush=False))
class _SessionContext(object):
def __init__(self):
self._level = 0
def __enter__(self):
if self._level == 0:
self._session = _Session()
self._level += 1
return self._session
def __exit__(self, type_, value, traceback):
self._level -= 1
if self._level == 0:
self._session.close()
self._session = None
_thread_local = local()
def get_session():
ctx = getattr(_thread_local, 'session_context', None)
if ctx:
return ctx
ctx = _SessionContext()
_thread_local.session_context = ctx
return ctx
def use(fun):
"""Decorator that creates SQLAlchemy session to use in inner method and
cleans it up afterwards. It is safe for nested calls.
Session is just closed, any commits or rollbacks must be handled
explicitly in a decorated method.
"""
def wrapper(*args, **kwargs):
with get_session():
return fun(*args, **kwargs)
return wrapper
# DB session wrappers for standard session functions. Add more as you see fit.
def query(*args, **kwargs):
return _Session().query(*args, **kwargs)
def add(*args, **kwargs):
return _Session().add(*args, **kwargs)
def add_all(*args, **kwargs):
return _Session().add_all(*args, **kwargs)
def delete(*args, **kwargs):
"""NOTE: DO NOT USE THIS DIRECTLY! USE obj.delete() instead."""
return _Session().delete(*args, **kwargs)
def execute(*args, **kwargs):
return _Session().execute(*args, **kwargs)
def flush(*args, **kwargs):
return _Session().flush(*args, **kwargs)
def commit(*args, **kwargs):
return _Session().commit(*args, **kwargs)
def rollback(*args, **kwargs):
return _Session().rollback(*args, **kwargs)
def close(*args, **kwargs):
return _Session().close(*args, **kwargs)
#########
# USAGE #
#########
@session.use
def handle_ajax1(...):
session.query(...)
session.commit()
@session.use
def handle_ajax2(...):
session.query(...)
session.commit()
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