C++ code that uses templates heavily is painful to compile, using 6 GiB of RAM is possible even for a "make -j1" build. It's kind of funny that a VPS with little RAM can build a full Linux kernel with all the modules and drivers, yet cannot build a small webserver. For big projects, the final linking process also eats enormous amount of RAM, it's possible for a small system to survive all the build and gets killed during the final linking.