performance - How to Reduce the time taken to load a pickle file in python

Question

I have created a dictionary in python and dumped into pickle. Its size went to 300MB. Now, I want to load the same pickle.

output = open('myfile.pkl', 'rb')
mydict = pickle.load(output)

Loading this pickle takes around 15 seconds. How can I reduce this time?

Hardware Specification: Ubuntu 14.04, 4GB RAM

The code bellow shows how much time takes to dump or load a file using json, pickle, cPickle.

After dumping, file size would be around 300MB.

import json, pickle, cPickle
import os, timeit
import json

mydict= {all values to be added}

def dump_json():    
    output = open('myfile1.json', 'wb')
    json.dump(mydict, output)
    output.close()    

def dump_pickle():    
    output = open('myfile2.pkl', 'wb')
    pickle.dump(mydict, output,protocol=cPickle.HIGHEST_PROTOCOL)
    output.close()

def dump_cpickle():    
    output = open('myfile3.pkl', 'wb')
    cPickle.dump(mydict, output,protocol=cPickle.HIGHEST_PROTOCOL)
    output.close()

def load_json():
    output = open('myfile1.json', 'rb')
    mydict = json.load(output)
    output.close()

def load_pickle():
    output = open('myfile2.pkl', 'rb')
    mydict = pickle.load(output)
    output.close()

def load_cpickle():
    output = open('myfile3.pkl', 'rb')
    mydict = pickle.load(output)
    output.close()


if __name__ == '__main__':
    print "Json dump: "
    t = timeit.Timer(stmt="pickle_wr.dump_json()", setup="import pickle_wr")  
    print t.timeit(1),'
'

    print "Pickle dump: "
    t = timeit.Timer(stmt="pickle_wr.dump_pickle()", setup="import pickle_wr")  
    print t.timeit(1),'
'

    print "cPickle dump: "
    t = timeit.Timer(stmt="pickle_wr.dump_cpickle()", setup="import pickle_wr")  
    print t.timeit(1),'
'

    print "Json load: "
    t = timeit.Timer(stmt="pickle_wr.load_json()", setup="import pickle_wr")  
    print t.timeit(1),'
'

    print "pickle load: "
    t = timeit.Timer(stmt="pickle_wr.load_pickle()", setup="import pickle_wr")  
    print t.timeit(1),'
'

    print "cPickle load: "
    t = timeit.Timer(stmt="pickle_wr.load_cpickle()", setup="import pickle_wr")  
    print t.timeit(1),'
'

Output :

Json dump: 
42.5809804916 

Pickle dump: 
52.87407804489 

cPickle dump: 
1.1903790187836 

Json load: 
12.240660209656 

pickle load: 
24.48748306274 

cPickle load: 
24.4888298893

I have seen that cPickle takes less time to dump and load but loading a file still takes a long time.

Answer 1

Try using the json library instead of pickle. This should be an option in your case because you're dealing with a dictionary which is a relatively simple object.

According to this website,

JSON is 25 times faster in reading (loads) and 15 times faster in writing (dumps).

Also see this question: What is faster - Loading a pickled dictionary object or Loading a JSON file - to a dictionary?

Upgrading Python or using the marshal module with a fixed Python version also helps boost speed (code adapted from here):

try: import cPickle
except: import pickle as cPickle
import pickle
import json, marshal, random
from time import time
from hashlib import md5

test_runs = 1000

if __name__ == "__main__":
    payload = {
        "float": [(random.randrange(0, 99) + random.random()) for i in range(1000)],
        "int": [random.randrange(0, 9999) for i in range(1000)],
        "str": [md5(str(random.random()).encode('utf8')).hexdigest() for i in range(1000)]
    }
    modules = [json, pickle, cPickle, marshal]

    for payload_type in payload:
        data = payload[payload_type]
        for module in modules:
            start = time()
            if module.__name__ in ['pickle', 'cPickle']:
                for i in range(test_runs): serialized = module.dumps(data, protocol=-1)
            else:
                for i in range(test_runs): serialized = module.dumps(data)
            w = time() - start
            start = time()
            for i in range(test_runs):
                unserialized = module.loads(serialized)
            r = time() - start
            print("%s %s W %.3f R %.3f" % (module.__name__, payload_type, w, r))

Results:

C:Python27python.exe -u "serialization_benchmark.py"
json int W 0.125 R 0.156
pickle int W 2.808 R 1.139
cPickle int W 0.047 R 0.046
marshal int W 0.016 R 0.031
json float W 1.981 R 0.624
pickle float W 2.607 R 1.092
cPickle float W 0.063 R 0.062
marshal float W 0.047 R 0.031
json str W 0.172 R 0.437
pickle str W 5.149 R 2.309
cPickle str W 0.281 R 0.156
marshal str W 0.109 R 0.047

C:pypy-1.6pypy-c -u "serialization_benchmark.py"
json int W 0.515 R 0.452
pickle int W 0.546 R 0.219
cPickle int W 0.577 R 0.171
marshal int W 0.032 R 0.031
json float W 2.390 R 1.341
pickle float W 0.656 R 0.436
cPickle float W 0.593 R 0.406
marshal float W 0.327 R 0.203
json str W 1.141 R 1.186
pickle str W 0.702 R 0.546
cPickle str W 0.828 R 0.562
marshal str W 0.265 R 0.078

c:Python34python -u "serialization_benchmark.py"
json int W 0.203 R 0.140
pickle int W 0.047 R 0.062
pickle int W 0.031 R 0.062
marshal int W 0.031 R 0.047
json float W 1.935 R 0.749
pickle float W 0.047 R 0.062
pickle float W 0.047 R 0.062
marshal float W 0.047 R 0.047
json str W 0.281 R 0.187
pickle str W 0.125 R 0.140
pickle str W 0.125 R 0.140
marshal str W 0.094 R 0.078

Python 3.4 uses pickle protocol 3 as default, which gave no difference compared to protocol 4. Python 2 has protocol 2 as highest pickle protocol (selected if negative value is provided to dump), which is twice as slow as protocol 3.