mapper.py

import multiprocessing
import time
import pymongo

start = time.time()

db = pymongo.MongoClient()['test']

def mapper(i):
    if i['a'] > 0.95:
        pass

pool_size = multiprocessing.cpu_count() * 2
pool = multiprocessing.Pool(pool_size)
pool.map(mapper, db.test.find(), chunksize=1000)
pool.close()
pool.join()
end = time.time()

print 'cost: ', end - start

original.py

mport pymongo
import time

db = pymongo.MongoClient()['test']
start = time.time()

for i in db.test.find():
    if i['a'] < 0.95:
        pass

end = time.time()

print 'cost: ', end - start