I purchase memory, 16G. But error occurred in process that c++: internal compiler error: Killed (program cc1plus). I use Docker executor.
Readers would probably need to see what you are doing in order to be able to advise you. You’ve upgraded your RAM, so it sounds like you are doing something memory-intensive, and the error sounds like the OS has kicked the process, probably due to running out of RAM.
Have you measured how much RAM this consumes when compiling on a dev machine?