>I think the error throw of the IntegrityError is totally expensive
>from both a DB perspective as well as a python perspective. if
>missing data is truly so rare then it might be fine, but the
>necessesity of then using SAVEPOINT seems to complicate things more
>than necessary. but you'd have to benchmark different scenarios to
>see which is best.
Thanks, but unfortunately, cannot get rid of tracebacks.
"""
from threading import Thread, Lock
from sqlalchemy import create_engine, MetaData, Table, Column, types,
schema, insert, update, delete
from sqlalchemy.orm import mapper, backref, scoped_session,
sessionmaker
from sqlalchemy.exceptions import IntegrityError
metadata = MetaData()
u_table = Table('auth_user', metadata, \
Column('id', types.Integer, primary_key=True), \
Column('username', types.String(30)))
f_table = Table('fs_file', metadata, \
Column('id', types.Integer, primary_key=True), \
Column('user_id', None, schema.ForeignKey("auth_user.id")), \
Column('path', types.String, unique=True), \
Column('ls', types.PickleType, nullable=False))
class User(object):
pass
mapper(User, u_table)
mapper(Path, f_table)
session = scoped_session(sessionmaker(transactional=True,
autoflush=False))
db = create_engine("postgres://...", strategy="threadlocal")
session.configure(bind=db)
db.echo = True
class LockingManager(object):
def __init__(self):
self._lock = Lock()
if not metadata.is_bound():
metadata.bind = db
def delete(self, uid=None):
self._lock.acquire()
try:
session.execute(delete(f_table), {'user_id': uid})
session.commit() #line 88
finally:
self._lock.release()
def insert(self, uid=None, path=None, ls=None):
...
def update(self, uid=None, path=None, ls=None):
...
def select(self, username=None):
stuff = session.query(User).filter_by(username=username).first()
return stuff
def arrange(Thread):
def __init__ (self, event, manager):
Thread.__init__(self)
self.e = event
self.manager = manager
def run(self):
theone = self.manager.select(username='me')
self.manager.delete(uid=theone.id)
...
class Watch(ProcessEvent):
def __init__(self, watch_manager, lock_manager):
self._watch_manager = watch_manager
self._lock_manager = lock_manager
def process_IN_DELETE(self, event):
super(Watch, self).process_default(event)
arrange(event, self._lock_manager).start()
def main():
lm = LockingManager()
wm = WatchManager()
wm.add_watch(HOMEDIR, mask, proc_fun=Watch(wm, lm), rec=True,
auto_add=True)
...
if (__name__ == "__main__"):
main()
"""
Traceback is happening on delete and always look like this:
"""
Traceback (most recent call last):
File "threading.py", line 442, in __bootstrap
self.run()
File "./camper.py", line 189, in run
walk(self.manager, theone, root)
File "./camper.py", line 101, in walk
manager.delete(uid=theone.id)
File "./camper.py", line 88, in delete
session.commit()
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/scoping.py",
line 74, in do
return getattr(self.registry(), name)(*args, **kwargs)
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/session.py",
line 484, in commit
self.transaction = self.transaction.commit()
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/session.py",
line 211, in commit
self.session.flush()
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/session.py",
line 686, in flush
self.uow.flush(self, objects)
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/
unitofwork.py", line 207, in flush
flush_context.execute()
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/
unitofwork.py", line 434, in execute
UOWExecutor().execute(self, head)
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/
unitofwork.py", line 1053, in execute
self.execute_save_steps(trans, task)
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/
unitofwork.py", line 1067, in execute_save_steps
self.save_objects(trans, task)
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/
unitofwork.py", line 1058, in save_objects
task.mapper.save_obj(task.polymorphic_tosave_objects, trans)
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/mapper.py",
line 1089, in save_obj
raise exceptions.ConcurrentModificationError("Updated rowcount %d
does not match number of objects updated %d" % (rows, len(update)))
ConcurrentModificationError: Updated rowcount 0 does not match number
of objects updated 1
"""
As far as I understand, one query at a time executing at a time now.
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