Linux上的“快速选择”（或类似的）实现？（而不是sortuniq-csort-rnhead-$n)

Question

GET /app1/public/pkg_e/v3/555413242345562/account/stats 401 954 5
GET /app1/public/pkg_e/v3/555412562561928/account/stats 200 954 97
GET /app1/secure/pkg_e/v3/555416251626403/ex/items/ 200 517 18
GET /app1/secure/pkg_e/v3/555412564516032/ex/cycle/items 200 32839 50
DELETE /app1/internal/pkg_e/v3/accounts/555411543532089/devices/bbbbbbbb-cccc-2000-dddd-43a8eabcdaa0 404 - 1
GET /app1/secure/pkg_e/v3/555412465246556/sessions 200 947 40
GET /app1/public/pkg_e/v3/555416264256223/account/stats 401 954 4
GET /app2/provisioning/v3/555412562561928/devices 200 1643 65
...

[root@srv112:~]$ N=6;cat test|awk '{print $1" "$2" ("$3")"}'\
|sed 's/[0-9a-f-]\+ (/%GUID% (/;s/\/[0-9]\{4,\}\//\/%USERNAME%\//'\
|sort|uniq -c|sort -rn|head -$N
      4 GET /app1/public/pkg_e/v3/%USERNAME%/account/stats (401)
      2 GET /app1/secure/pkg_e/v3/%USERNAME%/devices (200)
      2 GET /app1/public/pkg_e/v3/%USERNAME%/account/stats (200)
      2 DELETE /app1/internal/pkg_e/v3/accounts/%USERNAME%/devices/%GUID% (404)
      1 POST /app2/servlet/handler (200)
      1 POST /app1/servlet/handler (200)

如果我希望从同一个文件中找出最频繁的用户名，我会这样做：

[root@srv112:~]$ N=4;cat test|grep -Po '(?<=\/)[0-9]{4,}(?=\/)'\
|sort|uniq -c|sort -rn|head -$N
      9 555412562561928
      2 555411543532089
      1 555417257243373
      1 555416264256223

上面的内容对小型数据集很好，但是对于较大的输入集，sortuniq-csort-rnhead-$n的性能（复杂性）是无法忍受的（谈到~100台服务器，每台服务器~250个日志文件，每个日志文件~1MLN行）

尝试解决:sortuniq-c部分可以很容易地替换为awk1-liner，将其转换为：

|awk '{S[$0]+=1}END{for(i in S)print S[i]"\t"i}'|sort -rn|head -$N

3   tasty oranges
225 magic balls
17  happy dolls
15  misty clouds
93  juicy melons
55  rusty ideas
...

（给定n=3):

225 magic balls
93  juicy melons
55  rusty ideas

我可能会抓取示例Java代码并将其移植为以上的stdin格式（顺便说一句--对核心Java中缺少.quickselect(...)感到惊讶）--但是到处部署java-runtime的需求并不吸引人。我也许也可以获取它的示例（基于数组的）C代码片段，然后将其调整到上面的stdin格式，然后测试并修复泄漏等一段时间。甚至可以在awk中从头实现。但是（！）-超过1%的人可能会定期面临这个简单的需求--应该有一个标准的（预先测试的）实现？？希望...也许我用了错误的关键词来查找...

其他障碍：在处理大型数据集时还面临几个问题：

null

我目前的解决方案仍然不可靠，也不是最优的（正在进行中）看起来像：

find /logs/mount/srv*/tomcat/2013-09-24/ -type f -name "*_22:*"|\ 
# TODO: reorder 'find' output to round-robin through srv1 srv2 ...
#       to help 'parallel' work with multiple servers at once
parallel -P20 $"zgrep -Po '[my pattern-grep regexp]' {}\
|awk '{S[\$0]+=1}
END{for(i in S)if(S[i]>4)print \"count: \"S[i]\"\\n\"i}'"
# I throw away patterns met less than 5 times per log file
# in hope those won't pop on top of result list anyway - bogus
# but helps to address 16GB-mem problem for 'awk' below
awk '{if("count:"==$1){C=$2}else{S[$0]+=C}}
END{for(i in S)if(S[i]>99)print S[i]"\t"i}'|\
# I also skip all patterns which are met less than 100 times
# the hope that these won't be on top of the list is quite reliable
sort -rn|head -$N
# above line is the inefficient one I strive to address

Answer 1

我不确定编写自己的小工具是否可以接受，但您可以轻松地编写一个小工具，将sortuniq-csort-rnhead-$n-part替换为sortquickselect$n。该工具的好处是，它只读取第一个排序的输出一次，而且不需要在内存中保留太多数据。实际上，它只需要内存来保存当前行和顶部的$n行，然后打印这些行。

以下是QuickSelect.cpp:

#include <iostream>
#include <string>
#include <map>
#include <cstdlib>
#include <cassert>

typedef std::multimap< std::size_t, std::string, std::greater< std::size_t > > winner_t;
winner_t winner;
std::size_t max;

void insert( int count, const std::string& line )
{
    winner.insert( winner_t::value_type( count, line ) );
    if( winner.size() > max )
        winner.erase( --winner.end() );
}

int main( int argc, char** argv )
{
    assert( argc == 2 );
    max = std::atol( argv[1] );
    assert( max > 0 );
    std::string current, last;
    std::size_t count = 0;
    while( std::getline( std::cin, current ) ) {
        if( current != last ) {
            insert( count, last );
            count = 1;
            last = current;
        }
        else ++count;
    }
    if( count ) insert( count, current );
    for( winner_t::iterator it = winner.begin(); it != winner.end(); ++it )
        std::cout << it->first << " " << it->second << std::endl;
}

要用：

g++ -O3 quickselect.cpp -o quickselect