I'm trying to implement an algorithm able to search for multiple keys through ten huge files in Python (16 million of rows each one). I've got a sorted file with 62 million of keys, and I'm trying to scan each of the ten files in the dataset to look for a set key and their respective value.

This is a follow-up code on feedback from Scanning multiple huge files in Python. All files are encoded with UTF-8 and They should contain multiple language.

Here is a little slice of my sorted key file:

en Mahesh_Prasad_Varma
en Mahesh_Saheba
en maheshtala
en Maheshtala_College
en Mahesh_Thakur
en Maheshwara_Institute_Of_Technology
en Maheshwar_Hazari
en Just_to_Satisfy_You_(song) 1
en Just_to_See_Her 2
en Just_to_See_You_Smile 2
en Just_Tricking 1
en Just_Tricking! 1
en Just_Tryin%27_ta_Live 1
en Just_Until... 1
en Just_Us 1
en Justus 2
en Justus_(album) 2
en Zsófia_Polgár 1

Here is an example of some lines from one of my dataset files:

en Mahesh_Prasad_Varma 1
en maheshtala 1
en Maheshtala_College 1
en Maheshwara_Institute_Of_Technology 2
en Maheshwar_Hazari 1

Here is an example of the output file displaying a given key, maheshtala, which only appears once in the first file of the dataset:


The sorted_key file contains only unique keys obtained with cat and sort -u unix command on all of the ten dataset files. Each key can't be present more than once in a given dataset file, and each key can be present in more than one of the data files (not important I've to put zero if key is not in a specific file).

I've improved my new solution with multiprocessing module, and I'm now able to process each slice in 3 min, so it will take about 87 min to output final result (27+3*20 = 87 min against 447 min obtained before).

But due to a memory issue I'm not able to save the res dictionary. I'm sure that different processes have different address spaces and so all of them write to their own local copy of the dictionary. I'm forced to use Manager to share data between processes, obtaining worst performance. May I use queue?

Here it is the bash script I use to create sorted keys file.

#! /bin/bash
mkdir processed
mkdir processed/slice
cat $BASEPATH/dataset/* | cut -d' ' -f1,2 | sort -u -k2 > $BASEPATH/processed/sorted_keys
split -d -l 3000000 processed/sorted_keys processed/slice/slice-
for filename in processed/slice/*; do
    python processing.py $filename
rm $BASEPATH/processed/sorted_keys
rm -rf $BASEPATH/processed/slice

For each slice I launch processing.py Here is my working code, with Manager:

import os,sys,datetime,time,thread,threading;
from multiprocessing import Process, Manager

files_1 = ["20140601","20140602","20140603"]
files_2 = ["20140604","20140605","20140606"]
files_3 = ["20140607","20140608"]
files_4 = ["20140609","20140610"]

def split_to_elements(line):
    return line.split(" ")

def print_to_file():
    with open('processed/20140601','a') as output:
        for k in keys:
            splitted = split_to_elements(k)
            sum_count = 0
            clicks = ""
            while j < 10:
                click = res.get(k+"-"+str(j), 0)
                clicks += str(click) + ","
                sum_count += click
            to_print = str(sum_count) + "," + splitted[1] + "," + clicks + splitted[0]+ "\n"

def search_window(files,length):
    for f in files:
        with open("dataset/pagecounts-"+f) as current_file:
            for line in current_file:
                splitted = split_to_elements(line)
                res[splitted[0]+" "+splitted[1]+"-"+str(n)] = int(splitted[2].strip("\n"))

with open(sys.argv[1]) as sorted_keys:
    manager = Manager()
    res = manager.dict()
    keys = []
    print "STARTING POPULATING KEYS AT TIME: " + datetime.datetime.fromtimestamp(time.time()).strftime('%Y-%m-%d %H:%M:%S')
    for keyword in sorted_keys:
    print "ENDED POPULATION AT TIME: " + datetime.datetime.fromtimestamp(time.time()).strftime('%Y-%m-%d %H:%M:%S')
    print "STARTING FILES ANALYSIS AT TIME: " + datetime.datetime.fromtimestamp(time.time()).strftime('%Y-%m-%d %H:%M:%S')
    procs = []
    procs.append(Process(target=search_window, args=(files_1,0,)))
    procs.append(Process(target=search_window, args=(files_2,3,)))
    procs.append(Process(target=search_window, args=(files_3,6,)))
    procs.append(Process(target=search_window, args=(files_4,8,)))
    for p in procs:
    for p in procs:
    print "ENDED FILES ANALYSIS AT TIME: " + datetime.datetime.fromtimestamp(time.time()).strftime('%Y-%m-%d %H:%M:%S')
    print "START PRINTING AT TIME: " + datetime.datetime.fromtimestamp(time.time()).strftime('%Y-%m-%d %H:%M:%S')
    print "ENDED PRINT AT TIME: " + datetime.datetime.fromtimestamp(time.time()).strftime('%Y-%m-%d %H:%M:%S')

1 Answer 1


In your other post you state that you've already split the main key file, of 62 million entries, into multiple (20 or so) key file, and the code presented here is the one processing each of these files.

But as the keys from the key file is unique, you can avoid building the res dictionary and instead change the keys into storing only the information you need.

Going light on the current code

Regarding current code, you do use a lot of globals, which is not recommended, and you do use string concatenation with '+' which also is somewhat discussable. And some similar issues exists, but I'm going to leave them for now as you have a major performance issue to solve.

Suggestion for refactoring

  • Build the keys as a dictionary of counts – Instead of having keys to be an array, I would make this your main dictionary. Initialize it as a dictionary of lists/arrays. This is going to store the hit from each of the files, if present. As you need to know in which file the key was found, you could initialize the key with an array of 10 ints.

  • Process each dataset file – For each line get the key, and if present in keys add the count to the corresponding array index.

  • Print output file part – Traverse the keys dictionary, and for each key sum the corresponding array, print the information to the output file. Namely the sum of counts, the key, and each key.

This will result in a reduced memory print, which always is good. And you process the line only when traversing the line and not both there and in the output printing. The latter is a lot easier to do as you only traverse a prefilled array.

Disclaimer: I'm not sure how this is done using multiple processes, but you seem to have figured out that part already. If you're having issues with that, you could try this algorithm without the multiprocessing part.

PS! Are all of the processes writing to the same file in turns? It could(!) be better to allow each split to write to its own file, and join them afterwards...


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