Re: [Boost-users] why is this bzip2 boost code so slow?

14 Sep 2009

      ChristinaDRS wrote:
...
Hello,
This code with bzip2 takes 185 seconds to do 10000 iterations of compressing
and uncompressing. This seems way too high. When I replace the bzip2 code
with zlib code it take roughly 7 seconds. Anyone know what might be wrong?
[...]
...
int main()
{
    TimeType start_time = current_time();
    string compressed, received_data;
    boost::iostreams::filtering_streambufboost::iostreams::output out, in;
    const string send_data = "boo! how are you?";
for(int i = 0; i < 10000; ++i)
    {
  //compress
  out.push(boost::iostreams::bzip2_compressor());
  out.push(boost::iostreams::back_inserter(compressed));
  boost::iostreams::copy(boost::make_iterator_range(send_data), out);
  const string compressed1=compressed;
  //decompress
  received_data = decompress(compressed);
    }
    cout << "time elapsed: " << elapsed_seconds(start_time) << endl;
}
Isn't this line a bit of a problem?
...
out.push(boost::iostreams::back_inserter(compressed));
Basically, with each iteration you add more data to the string 
"compressed". I can't tell you why zip is so much faster, but I guess it 
somehow ignores the additional bytes where bzip doesn't.

I also think the previous line should not be inside the for-loop. Not 
sure about the effect, though. I am a bit surprised that it doesn't die 
with an exception.

With the main function below, I have 10000 iterations in less than a 
second on my old machine :-)

<snip>
int main()
{
     TimeType start_time = current_time();
     string compressed, received_data;
     boost::iostreams::filtering_streambufboost::iostreams::output 
out, in;
     const string send_data = "boo! how are you?";
     out.push(boost::iostreams::bzip2_compressor());

     for(int i = 0; i < 10000; ++i)
     {
         compressed.clear();
         //compress
         out.push(boost::iostreams::back_inserter(compressed));
         boost::iostreams::copy(boost::make_iterator_range(send_data), out);
         //decompress
         received_data = decompress(compressed);
     }
     cout << "time elapsed: " << elapsed_seconds(start_time) << endl;
}
</snip>

Regards,

Roland

Re: [Boost-users] why is this bzip2 boost code so slow?

Roland Bock