python-pyramid app memory is not releasing at all

Tags:

How to solve this memory leak?

What measures should I take to cleanup old session objects? Isn't session.close() is sufficient?

Is it something to do with pyramid?

Sqlalchmey setup:
----------------------------------------------------------------------------------
def get_db(request):
    maker = request.registry.dbmaker
    session = maker()

    @profile
    def cleanup(request):
        _session = request.db
        if request.exception is not None:
            _session.rollback()
        else:
            _session.commit()
        _session.close()
        # del _session     # No memory released

    request.add_finished_callback(cleanup)
    return session

def main(global_config, **settings):
    :
    :
    config.registry.dbmaker = sessionmaker(bind=engine)
    config.add_request_method(get_db, name='db', reify=True)
    :
    :

Pyramid app request handler is like

@view_config(route_name='list_employees', renderer='json')
def employees(request):
   session = request.db
   office = session.query(Office).get(1)
   employees = [x.name for x in office.employees]
   return employees

Now the problem is, In every request to list_employees the memory is growing. the size of increase in memory is almost equal to size of office.employees.

Debug:

request 1 starts with memory utilization = 10MB
request 1 ends with memory utilization = 18MB

request 2 starts with memory utilization = 18MB
request 2 ends with memory utilization = 26MB        

request 3 starts with memory utilization = 26MB
request 3 ends with memory utilization = 34MB        
                 :
                 :
           Grows eventually

employees = [x.name for x in office.employees]
This is the line where about 8-10MB memory utilized

To debug, I added __del__ method in Employ and Office models, looks like they are deleting.

Also tried session.expunge(office), del office and gc.collect()

I am debugging memory consumption using https://pypi.python.org/pypi/memory_profiler Also I am using https://pypi.python.org/pypi/transaction is other requests.

Not using debug pyramid toolbar.

EDIT : Found memory increase at this line (employees = [x.name for x in office.employees]) shows zero after 6-7 requests. But query was returning same number of rows.

EDIT : Added standalone app https://github.com/Narengowda/pyramid_sqlalchemy_app

EDIT: ITS NOT RELATED TO SQLALCHEMY AT ALL(my bad). Wrote a simple view function which doesn't have any sqlalchmey queries.

class Test(object):

    def __init__(self):
        self.x = 'sdfklhasdjkfhasklsdkjflksdfksd' *1000
        self.y = 'sdfklhasdjkfhasklsdkjflksdfksd' *1000
        self.z = 'sdfklhasdjkfhasklsdkjflksdfksd' *1000
        self.i = 'sdfklhasdjkfhasklsdkjflksdfksd' *1000
        self.v = 'sdfklhasdjkfhasklsdkjflksdfksd' *1000
        self.o = 'sdfklhasdjkfhasklsdkjflksdfksd' *1000


@view_config(route_name='home', renderer='json')
def my_view(request):
    return test(request)

@profile
def test(request):
    count = request.GET.get('count')
    l = [Test() for i in range(int(count))]
    print l[0]
    return {}

I am able to see this, below are the logs of requests