std :: unordered_map或普通std :: map具有更好的性能 [英] Which has better performance, std::unordered_map or normal std::map

问题描述

大家好，

考虑到插入和查找，我只是想知道这些数据结构中哪个具有更好的性能.从一些文章和论坛帖子中，我可以了解到unordered_map具有更好的性能.

I just want to know which of these data structure has better performance considering the insert and find. From some of the articles and forum posts I can understand that unordered_map has better performance.

但是当我使用V型放大器对它进行测试时，我发现并没有太大的差异.

But when I tested it using V-tune amplifier I don't find lot of differences.

我正在插入4000万个要映射的对象，键值的类型为< long long，指向对象的指针-64位>.以下是用于测试的代码段.

I am inserting 40 million objects to map, key-value has type of <long long, Pointer to object - 64 bit>. Following are the code snippets used for testing.

法线贴图:

        for(long long n = 0; n< nCount; n ++)
        {
            testMap.insert(std :: make_pair(n，pObject));
        }

        for (long long n = 0; n < nCount; n++)
        {
            testMap.insert(std::make_pair(n, pObject));
        }

Unorderd_map插入:

Unorderd_map inserts:

两者都占用了将近22到23秒的CPU时间.我可以看到负载计数(V-Tune放大器计数器)的显着差异.法线贴图的加载量为59.4亿，unordered_map的加载量为13.38亿.但考虑到内存限制，法线贴图为48.8％ unodered_map是80.9％.我认为即使在无序映射的情况下负载也更少，它更多的是受内存限制的应用程序，因此最终两者都具有相同的性能.

Both are taking almost 22 to 23 seconds of cpu time. I can see significant difference in load count (V-Tune amplifier counter) . Normal map has 5940 million loads and unordered_map has 1338 million loads. But considering the memory bound, normal map is 48.8% and unodered_map is 80.9%. I think even the loads are less in case of unordered map it is more a memory bound application, so finally both become same kind of performance.

 测试结果是在相同负载和相同环境下5次尝试的平均值.我正在使用Visual C ++ 2015、64位和Windows 7.

 Test results are the average of 5 attempts in same load and same environment. I am using Visual C++ 2015, 64 bit and windows 7.

从我所有的测试中，我无法得出结论，专家可以请您帮助我找到结论.哪个是更好的法线贴图或unordered_map.

from all my tests, I cannot come to a conclusion, experts could you please help me to find a conclusion. Which is better normal map or unordered_map.

感谢&问候

补充

推荐答案

2016年10月23日4:20，Renish Parambath写道:

On 10/23/2016 4:20 AM, Renish Parambath wrote:

法线贴图:

        for(long long n = 0; n< nCount; n ++)
        {
            testMap.insert(std :: make_pair(n，pObject));
        }

Normal map inserts:

        for (long long n = 0; n < nCount; n++)
        {
            testMap.insert(std::make_pair(n, pObject));
        }

我怀疑，通过对键进行排序，您可能正在为std :: map行使最佳情况，而不是一般情况.尝试先随机改组密钥.

I suspect that, by having the keys ordered, you may be exercising the best case for std::map, rather than the average case. Try randomly shuffling the keys first.

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