Re: [Haskell-cafe] serializing large data structures, stack overflow

7 Mar 2009


      import Data.Binary and then write a variant of something like how
Maps are currently serialised:

    instance (Ord k, Binary k, Binary e) => Binary (Map.Map k e) where
        put m = put (Map.size m) >> mapM_ put (Map.toAscList m)
        get   = liftM Map.fromDistinctAscList get

So you might want something that avoids flattening it to a list first

-- Don

frigginfriggins:
...
can you link to a good example of writing your own because I couldn't find one.
On Sat, Mar 7, 2009 at 8:57 PM, Don Stewart  wrote:
Increase the stack size, or use a different serialiser (they're only a
    half dozen lines to write), or different data structure?
-- Don
frigginfriggins:
    > I'm playing around with Netflix, implementing a simple KNN-algorithm, I
    will
    > later try SVD which seems to be the most successful approach.
    >
    > Using a database like Postgresqk is to slow so I want to serialize a
    > datastructure containing the ratings. I'm not sure about the
    > representation I will use just yet, if I should use multiple arrays or an
    Map/
    > IntMap.
    >
    > However I tried Data.Binary and already for small sizes I get stack
    overflow
    > when deserializing.
    > The serializing works fine but when bringing it back it overflows.
    > How can I solve this? This is just 2MB, I will eventually need soemthing
    like
    > 2-500MB to store everything depending on what representatin I choose.
    >
    > module Serialize where
    > import qualified Data.Binary as B
    > import qualified Data.Binary.Put as P
    > import qualified Data.Map as M
    > import qualified Data.List as L
    >
    > genTest :: Int -> M.Map (Int,Int) Int
    > genTest n = let movies = take n $ repeat 1
    >                 grades = take n $ repeat 4 in
    >             M.fromList $ ([1..n] `zip` movies) `zip` grades
    >
    > main = do
    >   let a = genTest 50000
    >   B.encodeFile "C:/users/saftarn/desktop/bintest.txt" a
    >   print "Success"
    >
    > dec = B.decodeFile "C:/users/saftarn/desktop/bintest.txt" >>= \a ->
    >       return $ (a :: M.Map (Int,Int) Int)
    >
    >
    >
    >
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