Haskell (ghc) runtime memory usage or what do I do wrong

Question

I wrote a small program, kind of specialized HTTP server in haskell, which is not much more complex than the code below. What puzzles me is its memory consumption. Say, when I run a test compiled from the enclosed code and make several POST requests containing up to 20Mb body whole program will have VM size of ~800Mb and this sounds odd. And this space is not returned to system if I leave an instance of such program running idle.

What does this mean?

import System.IO
import Network.HTTP.Server
import Network.Socket
import Network.URL


handler :: SockAddr -> URL -> Request String -> IO (Response String)
handler sa url rq = do
  writeFile "/tmp/out" (rqBody rq)
  return $ insertHeader HdrContentLength "0" (respond OK :: Response String)

main = serverWith defaultConfig {srvPort = 2121} handler

Answer 1

Firstly, you're using String . This is an inefficient representation for lots of data; the cost is something like 20 bytes per character. You should use ByteString (in the Data.ByteString / Data.ByteString.Char8 modules in the package bytestring ) instead.

Secondly, GHC up to and including version 6.12 doesn't return memory to the OS. However the upcoming GHC 7.0 will do this, so try with the latest release candidate .