map hash_map unordered_map 性能比较

原文地址http://blog.chinaunix.net/uid-20384806-id-3055333.html

by zieckey

测试条件：

gcc version 4.2.1 20070719  [FreeBSD]

FreeBSD  7.2-RELEASE #0: Fri May  1 07:18:07 UTC 2009     [e-mail]:/usr/obj/usr/src/sys/GENERIC  amd64
Intel(R) Xeon(R) CPU           E5620  @ 2.40GHz 16核

测试程序说明：

先准备好n个字符串随机的MD5字符串做为key，然后分别对3个容器进行插入、遍历、查找、删除操作。

例如，n=100的时候，插入是指插入100个随机MD5 key；遍历是指对容器遍历一次；查找是指分别对这个100个随机的MD5 key做查找操作（即查找100次）；删除是指挨个删除这个100个随机MD5 key。

测试数据如下表：

插入，单位us1001K10K100K1M10Mstd::map241283335888381214443908862233380std::ext/hash_map97166716466146025178844618512639std::tr1::unordered_map777728052530946583127429297

遍历，单位us1001K10K100K1M10Mstd::map1176842116031557001771906std::ext/hash_map474304218398804703444781575std::tr1::unordered_map112121

查找，单位us1001K10K100K1M10Mstd::map156211130456258709410026059064394std::ext/hash_map777748056569746602317705527std::tr1::unordered_map777728051544566595377600263

删除，单位us1001K10K100K1M10Mstd::map291364149584472414667589792491113std::ext/hash_map8986990688652496476710372650std::tr1::unordered_map494804879330873950984369617

结论：

1. std::tr1::unordered_map 与 std::ext/hash_map 

     任何情况下，如果要在这两个容器之间选择的话，我们毫不犹豫应该选择 unordered_map。因为他的性能在上述4中操作中均优于 hash_map，甚至可以说远远优于 hash_map。

2. std::tr1::unordered_map 与 std::map 

     map的性能总体来说是最差的。但是，当我们需要一个有序的关联容器的时候，我们必须选择std::map，因为 unordered_map 内部元素不是有序的，这一点从名字都可以看出来。除此之外都应该选择 unordered_map 。

3. 上述测试中，unordered_map 的遍历性能几乎是常数级别的，与常识不太相符，需要再研究研究。

附录：贴上源代码

说明：与测试程序稍有区别，这里的源码里没有MD5相关的代码以确保其他人能比较方便的直接拿去编译运行。

如有错误还请跟帖指出，非常感谢。

#include <iostream>#include <string>#include <sstream>#include <list>#include <map>#include <sys/time.h>#include <ext/hash_map>#include <tr1/unordered_map>namespace zl{ //{{{    struct equal_to    {        bool operator()(const char* s1, const char* s2) const        {            return strcmp(s1, s2) == 0;        }    };     struct hash_string        : public std::unary_function<std::string, std::size_t>        {            std::size_t                operator()(const std::string& __s) const#ifdef __linux__                { return std::tr1::Fnv_hash<>::hash(__s.data(), __s.length()); }#else                { return std::tr1::_Fnv_hash<>::hash(__s.data(), __s.length()); }#endif        };        struct hash_charptr        : public std::unary_function<const char*, std::size_t>        {            std::size_t                operator()(const char* __s) const#ifdef __linux__                { return std::tr1::Fnv_hash<>::hash(__s, strlen(__s)); }#else                { return std::tr1::_Fnv_hash<>::hash(__s, strlen(__s)); }#endif        };}//}}}typedef std::list<std::string> string_list;typedef std::map<std::string, int> string_map;typedef __gnu_cxx::hash_map<std::string, int, zl::hash_string> string_hash_map;typedef std::tr1::unordered_map<std::string, int> string_unordered_map;void fill_list(string_list& slist, size_t count);uint64_t current_usec();int main( int argc, char* argv[] ){    if (argc != 2 && argc != 3)    {        fprintf(stderr, "Usage:%s test_count rehash\n", argv[0]);        fprintf(stderr, "For example:%s 10000 rehash\n", argv[0]);        return -1;    }    size_t count = atoi(argv[1]);    bool rehash = false;    if (argc == 3)    {        rehash = true;    }    string_map smap;    string_hash_map shash_map;    string_unordered_map sunordered_map;    if (rehash)    {        sunordered_map.rehash(count);    }    string_list slist;    fill_list(slist, count);    uint64_t start = 0;    uint64_t end = 0;    uint64_t map_insert_us = 0;    uint64_t hash_map_insert_us = 0;    uint64_t unordered_map_insert_us = 0;    uint64_t map_traverse_us = 0;    uint64_t hash_map_traverse_us = 0;    uint64_t unordered_map_traverse_us = 0;    uint64_t map_find_us = 0;    uint64_t hash_map_find_us = 0;    uint64_t unordered_map_find_us = 0;    uint64_t map_delete_us = 0;    uint64_t hash_map_delete_us = 0;    uint64_t unordered_map_delete_us = 0;    // Insert test    {//{{{        string_list::iterator it(slist.begin());        string_list::iterator ite(slist.end());        //map insert        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            smap[*it] = i;        }        end = current_usec();        map_insert_us = end - start;        //hash_map insert        it = slist.begin();        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            shash_map[*it] = i;        }        end = current_usec();        hash_map_insert_us = end - start;        //unordered_map insert        it = slist.begin();        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            shash_map[*it] = i;        }        end = current_usec();        unordered_map_insert_us = end - start;    }//}}}    // Traverse test    {//{{{        //map traverse         {            string_map::iterator it(smap.begin());            string_map::iterator ite(smap.end());            start = current_usec();            for (int i = 0; it != ite; ++it)            {                i++;            }            end = current_usec();            map_traverse_us = end - start;        }        //hash_map traverse         {            string_hash_map::iterator it(shash_map.begin());            string_hash_map::iterator ite(shash_map.end());            start = current_usec();            for (int i = 0; it != ite; ++it)            {                i++;            }            end = current_usec();            hash_map_traverse_us = end - start;        }        //unordered_map traverse         {            string_unordered_map::iterator it(sunordered_map.begin());            string_unordered_map::iterator ite(sunordered_map.end());            start = current_usec();            for (int i = 0; it != ite; ++it)            {                i++;            }            end = current_usec();            unordered_map_traverse_us = end - start;        }    }//}}}    // Find test    {//{{{        string_list::iterator it(slist.begin());        string_list::iterator ite(slist.end());        //map find        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            smap[*it] = i;        }        end = current_usec();        map_find_us = end - start;        //hash_map find        it = slist.begin();        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            shash_map[*it] = i;        }        end = current_usec();        hash_map_find_us = end - start;        //unordered_map find        it = slist.begin();        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            shash_map[*it] = i;        }        end = current_usec();        unordered_map_find_us = end - start;    }//}}}    // Delete test    {//{{{        string_list::iterator it(slist.begin());        string_list::iterator ite(slist.end());        //map delete        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            smap.erase(*it);        }        end = current_usec();        map_delete_us = end - start;        //hash_map delete        it = slist.begin();        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            shash_map.erase(*it);        }        end = current_usec();        hash_map_delete_us = end - start;        //unordered_map delete        it = slist.begin();        start = current_usec();        for (int i = 0; it != ite; ++it, ++i)        {            shash_map.erase(*it);        }        end = current_usec();        unordered_map_delete_us = end - start;    }//}}}    //stat output    std::cout << " insert, count " << count << std::endl;    std::cout << " std::map " << map_insert_us << " us\n";    std::cout << " std::ext/hash_map " << hash_map_insert_us << " us\n";    std::cout << "std::tr1::unordered_map " << unordered_map_insert_us << " us\n";    std::cout << "\n";    std::cout << " traverse, count " << count << std::endl;    std::cout << " std::map " << map_traverse_us << " us\n";    std::cout << " std::ext/hash_map " << hash_map_traverse_us << " us\n";    std::cout << "std::tr1::unordered_map " << unordered_map_traverse_us << " us\n";    std::cout << "\n";    std::cout << " find, count " << count << std::endl;    std::cout << " std::map " << map_find_us << " us\n";    std::cout << " std::ext/hash_map " << hash_map_find_us << " us\n";    std::cout << "std::tr1::unordered_map " << unordered_map_find_us << " us\n";    std::cout << "\n";    std::cout << " delete, count " << count << std::endl;    std::cout << " std::map " << map_delete_us << " us\n";    std::cout << " std::ext/hash_map " << hash_map_delete_us << " us\n";    std::cout << "std::tr1::unordered_map " << unordered_map_delete_us << " us\n";         return 0;}void fill_list(string_list& slist, size_t count){    for (size_t i = 0; i < count; ++i)    {        std::ostringstream oss;        oss << i;        //slist.push_back(MD5::getHexMD5(oss.str().c_str(), oss.str().length()));        slist.push_back(oss.str());    }}uint64_t current_usec(){    struct timeval tv;    gettimeofday( &tv, NULL );    return tv.tv_sec * 1000 * 1000 + tv.tv_usec;}