One article to understand the problem of large file sorting/external memory sorting

#!/usr/bin/python2.7

import time

def readline_by_yield(bfile):
    with open(bfile, 'r') as rf:
        for line in rf:
            yield line

def quick_sort(lst):
    if len(lst) < 2:
        return lst
    pivot = lst[0]
    left = [ ele for ele in lst[1:] if ele < pivot ]
    right = [ ele for ele in lst[1:] if ele >= pivot ]
    return quick_sort(left) + [pivot,] + quick_sort(right)

def split_bfile(bfile):
    count = 0
    nums = []
    for line in readline_by_yield(bfile):
        num = int(line)
        if num not in nums:
            nums.append(num)
        if 10000 == len(nums):
            nums = quick_sort(nums)
            with open(&#39;subfile/subfile{}.txt&#39;.format(count+1),&#39;w&#39;) as wf:
                wf.write(&#39;\n&#39;.join([ str(i) for i in nums ]))
            nums[:] = []
            count += 1
            print count

now = time.time()
split_bfile(&#39;total.txt&#39;)
run_t = time.time()-now
print &#39;Runtime : {}&#39;.format(run_t)

#!/usr/bin/python2.7
# -*- coding: utf-8 -*-

import os
import time

testdir = '/ssd/subfile'

now = time.time() 

# Step 1 : 获取全部文件描述符
fds = []
for f in os.listdir(testdir):
    ff = os.path.join(testdir,f)
    fds.append(open(ff,'r'))

# Step 2 : 每个文件获取第一行，即当前文件最小值
nums = []
tmp_nums = []
for fd in fds:
    num = int(fd.readline())
    tmp_nums.append(num)

# Step 3 : 获取当前最小值放入暂存区，并读取对应文件的下一行；循环遍历。
count = 0
while 1:
    val = min(tmp_nums)
    nums.append(val)
    idx = tmp_nums.index(val)
    next = fds[idx].readline()
    # 文件读完了
    if not next:
        del fds[idx]
        del tmp_nums[idx]
    else:
        tmp_nums[idx] = int(next)
    # 暂存区保存1000个数，一次性写入硬盘，然后清空继续读。
    if 1000 == len(nums):
        with open('final_sorted.txt','a') as wf:
            wf.write('\n'.join([ str(i) for i in nums ]) + '\n')
        nums[:] = []
    if 499999999 == count:
        break
    count += 1
   
with open('runtime.txt','w') as wf:
    wf.write('Runtime : {}'.format(time.time()-now))

# 方法一：手动计算
 
In [62]: ip
Out[62]: '10.3.81.150'
 
In [63]: ip.split('.')[::-1]
Out[63]: ['150', '81', '3', '10']
 
In [64]: [ '{}-{}'.format(idx,num) for idx,num in enumerate(ip.split('.')[::-1]) ]
Out[64]: ['0-150', '1-81', '2-3', '3-10']
 
In [65]: [256**idx*int(num) for idx,num in enumerate(ip.split('.')[::-1])]
Out[65]: [150, 20736, 196608, 167772160]
 
In [66]: sum([256**idx*int(num) for idx,num in enumerate(ip.split('.')[::-1])])                     
Out[66]: 167989654 
In [67]:
 
# 方法二：使用C扩展库来计算
In [71]: import socket,struct
In [72]: socket.inet_aton(ip)
Out[72]: b'\n\x03Q\x96'
 
In [73]: struct.unpack("!I", socket.inet_aton(ip))
# !表示使用网络字节顺序解析, 后面的I表示unsigned int, 对应Python里的integer or long 
Out[73]: (167989654,)
 
In [74]: struct.unpack("!I", socket.inet_aton(ip))[0]
Out[74]: 167989654
 
In [75]: socket.inet_ntoa(struct.pack("!I", 167989654))              
Out[75]: '10.3.81.150'
 
In [76]:

def readline_by_yield(bfile):
    with open(bfile, 'r') as rf:
        for line in rf:
            yield line

def split_bfile(bfile):
    count = 0
    d = {}
    for line in readline_by_yield(bfile):
        line = line.strip()
        if line not in d:
            d[line] = 0
        d[line] += 1
        if 10000 == len(d):
            text = ''
            for string in sorted(d):
                text += '{}\t{}\n'.format(string,d[string])
            with open('subfile/subfile{}.txt'.format(count+1),'w') as wf:
                wf.write(text.strip())
            d.clear()
            count += 1

    text = ''
    for string in sorted(d):
        text += '{}\t{}\n'.format(string,d[string])
    with open('subfile/subfile_end.txt','w') as wf:
        wf.write(text.strip())

split_bfile('bigfile.txt')

import os
import json
import time
import traceback

testdir = '/ssd/subfile'

now = time.time() 

# Step 1 : 获取全部文件描述符
fds = []
for f in os.listdir(testdir):
    ff = os.path.join(testdir,f)
    fds.append(open(ff,'r'))

# Step 2 : 每个文件获取第一行
tmp_strings = []
tmp_count = []
for fd in fds:
    line = fd.readline()
    string,count = line.strip().split('\t')
    tmp_strings.append(string)
    tmp_count.append(int(count))

# Step 3 : 获取当前最小值放入暂存区，并读取对应文件的下一行；循环遍历。
result = []
need2del = []

while True:
    min_str = min(tmp_strings)
    str_idx = [i for i,v in enumerate(tmp_strings) if v==min_str]
    str_count = sum([ int(tmp_count[idx]) for idx in str_idx ])
    result.append('{}\t{}\n'.format(min_str,str_count))
    for idx in str_idx:
        next = fds[idx].readline()  # IndexError: list index out of range
        # 文件读完了
        if not next:
            need2del.append(idx)
        else:
            next_string,next_count = next.strip().split('\t')
            tmp_strings[idx] = next_string
            tmp_count[idx] = next_count
    # 暂存区保存10000个记录，一次性写入硬盘，然后清空继续读。
    if 10000 == len(result):
        with open('merged.txt','a') as wf:
            wf.write(''.join(result))
        result[:] = []
    # 注意: 文件读完需要删除文件描述符的时候, 需要逆序删除
    need2del.reverse()
    for idx in need2del:
        del fds[idx]
        del tmp_strings[idx]
        del tmp_count[idx]
    need2del[:] = []
    if 0 == len(fds):
        break

with open('merged.txt','a') as wf:
    wf.write(''.join(result))
result[:] = []

import time

def read_line(filepath):
    with open(filepath,'r') as rf:
        for line in rf:
            yield line

start_ts = time.time()

max_str = None
max_count = 0
for line in read_line('merged.txt'):
    string,count = line.strip().split('\t')
    if int(count) > max_count:
        max_count = int(count)
        max_str = string

print(max_str,max_count)
print('Runtime {}'.format(time.time()-start_ts))