[Haskell-cafe] Data.Binary suboptimal instance

[Henning Thielemann]

Khudyakov Alexey schrieb:
> On Saturday 23 May 2009 02:55:17 Antoine Latter wrote:
>> Or you could go for the compromise position, where the list can be
>> part of a complex data structure so you're not relying on EOF to find
>> the end.
>>
> Interesting solution however it does not perform very nice. I wrote
> microbenchmark
>
>> xs :: [Word32]
>> xs = [1..(10^6)]
>
> Writing chunked list of Word32
>> B.writeFile "chunked" . toLazyByteString . putList putWord32be $ xs
> real    0m4.311s
> user    0m3.272s
> sys     0m0.096s
>
> Reading chunked list of Word32
>> print . last . runGet (getList getWord32be) =<< B.readFile "chunked"
> real    0m0.634s
> user    0m0.496s
> sys     0m0.012s
>
>
> Writing stream of Word32
>> B.writeFile "stream" . encodeStream $ xs
> real    0m0.391s
> user    0m0.252s
> sys     0m0.020s
>
> Reading stream of Word32
>> print . (last :: [Word32] -> Word32) . decodeStream =<< B.readFile "stream"
> real    0m0.376s
> user    0m0.248s
> sys     0m0.020s
>
>
> I didn'd do any profiling so I have no idea why writing is so slow.


If you use top-level definition 'xs' the program might cache the list
and second write is faster. You may change the order of tests in order
check, whether that is the cause.