multiprocessing - pyodbc IOError: bad message length - python-2.7

Question

I am unexpectedly getting IOError: bad message length error when trying to share pyodbc connection across multiple processes, especially when N is more than 4 (no. of cores). Sometimes I also get cPickle.UnpicklingError: invalid load key, '#'., pyodbc.ProgrammingError: ('24000', '[24000] [FreeTDS][SQL Server]Invalid cursor state (0) (SQLExecDirectW)') as errors.
# Import custom python packages
import multiprocessing
import multiprocessing.managers as mm
import pathos.multiprocessing as mp
import pyodbc, datetime, time
class MyConn(object):
def __init__(self):
self.conn = None
self.cursor = None
def connect_to_db(self):
self.conn = pyodbc.connect("DSN=cpmeast;UID=dntcore;PWD=dntcorevs2")
self.cursor = self.conn.cursor()
def run_qry(self, data):
print 'Running query', data
self.cursor.execute("WAITFOR DELAY '00:00:01';select GETDATE(), '"+str(data)+"';")
l = self.cursor.fetchall()
_l = []
for i in l:
_l.append(list(i))
print 'Result for query', data, _l
return _l
class MyManagerClass(object):
def __init__(self):
self.result = multiprocessing.Manager().list()
def read_data(self, *args):
conn = args[0][0]
data = args[0][1]
l = conn.run_qry(data)
self.result.append(l)
class MyManager(mm.BaseManager):
pass # Pass is really enough. Nothing needs to be done here.
def main():
time_start = time.time()
MyManager.register("MyConn", MyConn)
manager = MyManager()
manager.start()
a = manager.MyConn()
a.connect_to_db()
dbm = MyManagerClass()
pool = mp.ProcessingPool(4)
jobs = []
N = 5
for i in range(N):
jobs.append((a, str(i)))
for i in pool.imap(dbm.read_data, jobs):
print 'result'
pool.close()
pool.join()
print 'Result', dbm.result
print 'Closed'
time_stop = time.time()
msg = 'runtime: {0}'.format(str(datetime.timedelta
(seconds=time_stop-time_start)))
print msg
if __name__ == '__main__':
main()