增强二进制存档-减小大小 [英] Boost binary archives - reducing size

问题描述

我正在尝试减小C ++中boost存档的内存大小.

I am trying to reduce the memory size of boost archives in C++.

我发现的一个问题是，Boost的二进制归档文件默认对任何int使用4个字节，而不管其大小如何.因此，我得到一个空的boost二进制归档文件占用62个字节，而一个空的文本归档文件占用40个字节(一个空文本归档文件的文本表示:22 serialization::archive 14 0 0 1 0 0 0 0 0).

One problem I have found is that Boost's binary archives default to using 4 bytes for any int, regardless of its magnitude. For this reason, I am getting that an empty boost binary archive takes 62 bytes while an empty text archive takes 40 (text representation of an empty text archive: 22 serialization::archive 14 0 0 1 0 0 0 0 0).

是否有任何方法可以更改此int的默认行为?

Is there any way to change this default behavior for ints?

否则，除了对向量使用make_array之外，还有其他方法可以优化二进制归档文件的大小吗?

Else, are there any other ways to optimize the size of a binary archive apart from using make_array for vectors?

推荐答案

问. 我正在尝试减小C ++中Boost存档的内存大小.

请参见提高C ++序列化的开销

问. 我发现的一个问题是，Boost的二进制归档文件默认对任何int使用4个字节，而不论其大小如何.

那是因为它是一个序列化库，而不是压缩库

That's because it's a serialization library, not a compression library

问. 由于这个原因，我得到一个空的boost二进制归档文件占用62个字节，而一个空的文本归档文件占用40个字节(一个空文本归档文件的文本表示形式:22序列化: :archive 14 0 0 1 0 0 0 0 0).

使用存档标志:例如来自 Boost序列化:如何预测序列化结果的大小?:

Use the archive flags: e.g. from Boost Serialization : How To Predict The Size Of The Serialized Result?:

• 调优(boost :: archive :: no_codecvt，boost :: archive :: no_header，

• Tune things (boost::archive::no_codecvt, boost::archive::no_header, disable tracking etc.)

问. 有什么办法可以更改int的默认行为?

不.不过有BOOST_IS_BITWISE_SERIALIZABLE(T)(有关示例和说明，请参见例如 Boost串行按位串行化).

No. There is BOOST_IS_BITWISE_SERIALIZABLE(T) though (see e.g. Boost serialization bitwise serializability for an example and explanations).

问. 还有，除了对向量使用make_array之外，还有其他方法可以优化二进制归档文件的大小吗?

Q. Else, are there any other ways to optimize the size of a binary archive apart from using make_array for vectors?

使用make_array对于vector<int>无效:

在Coliru上直播

#include <boost/archive/binary_oarchive.hpp>
#include <boost/serialization/vector.hpp>
#include <sstream>
#include <iostream>

static auto const flags = boost::archive::no_header | boost::archive::no_tracking;

template <typename T>
std::string direct(T const& v) {
    std::ostringstream oss;
    {
        boost::archive::binary_oarchive oa(oss, flags);
        oa << v;
    }
    return oss.str();
}

template <typename T>
std::string as_pod_array(T const& v) {
    std::ostringstream oss;
    {
        boost::archive::binary_oarchive oa(oss, flags);
        oa << v.size() << boost::serialization::make_array(v.data(), v.size());
    }
    return oss.str();
}

int main() {
    std::vector<int> i(100);
    std::cout << "direct: "       << direct(i).size() << "\n";
    std::cout << "as_pod_array: " << as_pod_array(i).size() << "\n";
}

打印

direct: 408
as_pod_array: 408

压缩

最直接的优化方法是压缩结果流(另请参阅添加的基准测试这里).

除非如此，否则您将不得不覆盖默认的序列化并应用您自己的压缩(可以是简单的行程编码，霍夫曼编码或更多特定于域的压缩).

Barring that, you will have to override default serialization and apply your own compression (which could be a simple run-length encoding, huffman coding or something more domain specific).

在Coliru上直播

#include <boost/archive/binary_oarchive.hpp>
#include <boost/serialization/vector.hpp>
#include <sstream>
#include <iostream>
#include <boost/iostreams/filter/bzip2.hpp>
#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/device/back_inserter.hpp>
#include <boost/iostreams/copy.hpp>

static auto const flags = boost::archive::no_header | boost::archive::no_tracking;

template <typename T>
size_t archive_size(T const& v)
{
    std::stringstream ss;
    {
        boost::archive::binary_oarchive oa(ss, flags);
        oa << v;
    }

    std::vector<char> compressed;
    {
        boost::iostreams::filtering_ostream fos;
        fos.push(boost::iostreams::bzip2_compressor());
        fos.push(boost::iostreams::back_inserter(compressed));

        boost::iostreams::copy(ss, fos);
    }

    return compressed.size();
}

int main() {
    std::vector<int> i(100);
    std::cout << "bzip2: " << archive_size(i) << "\n";
}

打印

bzip2: 47

这是〜11％的压缩率(如果删除存档标志，则为〜19％).

That's a compression ratio of ~11% (or ~19% if you drop the archive flags).

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