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map hash_map unordered_map 性能比较

2016-07-13 15:26 423 查看
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     root@driscoll.cse.buffalo.edu:/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us1001K10K100K1M10M
std::map241283335888381214443908862233380
std::ext/hash_map97166716466146025178844618512639
std::tr1::unordered_map777728052530946583127429297
遍历，单位us1001K10K100K1M10M
std::map1176842116031557001771906
std::ext/hash_map474304218398804703444781575
std::tr1::unordered_map112121
查找，单位us1001K10K100K1M10M
std::map156211130456258709410026059064394
std::ext/hash_map777748056569746602317705527
std::tr1::unordered_map777728051544566595377600263
删除，单位us1001K10K100K1M10M
std::map291364149584472414667589792491113
std::ext/hash_map8986990688652496476710372650
std::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;
}
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