[Haskell-cafe] performance of map reduce

[Manlio Perillo]

Hi again.

In 
http://book.realworldhaskell.org/read/concurrent-and-multicore-programming.html#id676390
there is a map reduce based log parser.

I have written an alternative version:
http://paste.pocoo.org/show/85699/

but, with a file of 315 MB, I have [1]:

1) map reduce implementation, non parallel
real	0m6.643s
user	0m6.252s
sys	0m0.212s

2) map reduce implementation, parallel with 2 cores
real	0m3.840s
user	0m6.384s
sys	0m0.652s

3) my implementation
real	0m8.121s
user	0m7.804s
sys	0m0.216s



What is the reason of the map reduce implementation being faster, even 
if not parallelized?

It is possible to implement a map reduce version that can handle gzipped 
log files?


[1] These tests does not consider the "first run".
For the first run (no data in OS cache), I have (not verified):

1) map reduce implementation, parallel with 2 cores
real	0m3.735s
user	0m6.328s
sys	0m0.604s

2) my implementation
real	0m13.659s
user	0m7.712s
sys	0m0.360s




Thanks   Manlio Perillo