Hi,
I'm hoping someone can help me with properly configuring a session/
transactions for multiple uses as I haven't been able to get it quite
right.
I've created a python module to contain my model classes and a
connection class. This module wil be imported by both single-use
scripts (run, then quit), long-running background scripts (run
passively while waiting for a new event), and imported into a
TurboGears app. I'm using PostgreSQL 8.4, SQLAlchemy 0.5.5, and
TurboGears 2.0.
After getting different types of transaction errors, e.g.
> InternalError: (InternalError) current transaction is aborted,
> commands ignored until end of transaction block
> InvalidRequestError: Can't reconnect until invalid transaction is
> rolled back"
> "A transaction is already begun. Use subtransactions=True "
> sqlalchemy.exc.InvalidRequestError: A transaction is already begun.
> Use subtransactions=True to allow subtransactions.
I settled on this in my db connection module, which is called by all
my scripts:
class MyDatabase:
def __init__(self, database_connection_string=None):
self.database_connection_string = database_connection_string
self.engine = create_engine(self.database_connection_string,
echo=False)
self.metadata = MetaData()
self.metadata.bind = self.engine
try:
db # singleton
except NameError:
db = MyDatabase()
engine = db.engine
metadata = db.metadata
Session = scoped_session(sessionmaker(bind=engine, autocommit=True,
autoflush=False))
Then in each script I import this module, create a new session:
session = Session()
and query like this:
if session.autocommit:
session.begin()
<do stuff that modifies the db, i.e. not just select statements>
session.commit()
I was hoping this is fairly bullet-proof, but unfortunately my
TurboGears app still hangs (with no error messages) after running for
some period of time, though I think it hangs when multiple queries hit
the database at the same time. I'm suspecting some kind of deadlock,
but that's just a guess.
I'm at a loss as to where the problem lies, but I wanted to check with
the experts here that I'm using SA appropriately. Any help/suggestions
greatly appreciated.
Cheers,
Demitri
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