performance, boost mmap files, fstream

[ameyav]

Hi,

MSVC 9
Boost 1.38

I have an existing program that reads text files a line at a time using the std::ifstream and istream& getline ( istream& is, string& str );

Typical file size is ~40mb

To increase the file reading performance i used boost::iostreams::mapped_file_source and tokenized the memory buffer using boost::algorithm::split with "\n" as delimiter

Before implementing this change in the main program i wrote this logic in a small test program and i found that using the boost memory mapped file is almost 50% faster than using std::fstream

However when i implemented the same logic in my main program i did not get the same performance improvement. [Note: I have taken care to ensure that no other logic in my main program is negating any performance gain achieved by using the memory mapped files]

/O2 and /GL are enabled

Size of small test program: 180K
Size of main program: 680K

I am using the /MT option to link to the boost libs

Can someone thow some light onto this behaviour please.

Thanks

Regards,
Ameya

[Banfa]

Not really except to say you rarely get best case potential improvement in a real life program.