{-# LANGUAGE BangPatterns #-} import qualified Data.Map as M import Debug.Trace {- I'm trying to run a HAppS web site with a large amount of data: stress testing happstutorial.com. Well, 20 million records doesn't sound that large by today's standards, but anyway that's my goal for now. I have a standard Data.Map.Map as the base structure for one of my macid data tables (jobs), but I noticed something that is probably causing problems for me. Even a simple 20 million record with int/int key values causes an out of memory error for me in ghci, on a computer with 256M of ram. I'm wondering if there is a data structure that might be more suitable for large recordsets. Or do you just have to use a database, or some sort of file-based serialization, once your records are in the millions? Or is this some weird subtlety of lazy evalution, or some other haskell gotcha? -} size = 2 * 10^7 -- out of memory error t = (M.! size) . myFromList . map (\i->(i,i)) $ [1..size] -- Lists are no problem {- *Main> :! time ghc -e tL testMap.hs (20000000,20000000) 3.38user 0.09system 0:03.53elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k -} tL = (!! (size-1)) . map (\i->(i,i)) $ [1..size] t2 = (M.fromList . map (\i->(i,i)) $ [1..10] ) M.\\ (M.fromList . map (\i->(i,i)) $ [6..15]) -- does this evaluate all of list l, or just whnf? myFromList (!l) = M.fromList l