Revisit iostream, ostringstream usages for performance #60
Description
We have iostream usages in the code, especially the IOUtil::to_value and to_string methods. We have seen that not using this at one critical path could change the throughput from 28000 to 33000. Also according to https://erdani.com/publications/cuj-2005-08.pdf iostreams are not really recommended. We may investigate this further.