I can env_set_mapsize(env, 1 GB) without any problems in linux.

But on windows, it is a different story
 
 Machine 1) Windows 64 only opens with upto 10 MB (apporx)
 Machine 2 Windows 64 only opens with upto 500 MB (apporx)
 Machine 3) Virtual box Windows 64 running on linux works with 1 GB

Q1) So why is this happening. Am I doing anything wrong.
Q2) And setting env_set_mapsize before calling open is not enough. I need to set
      env_set_mapsize(env, 0) just before beginning a write transaction inorder to
     insert something or otherwise the application indefinitely hangs on the second insert transaction.

Both the above questions concerns just Windows. Everything is fine with linux.