I'd suggest checking your JVM memory settings. The Haskell implementation may allow the heap to grow arbitrarily, but the default JVM heap size is very limited, which may result in poor memory performance.
On Feb 23, 12:51 am, "Edward Z. Yang" <ezy...@mit.edu> wrote: > I'd first like to state that I went into this exercise expecting > Bagwell's Hash Array Mapped Tries to blow the competition out of the > water; I'd get a fast functional map and give it to Haskell and people > would rejoice. > > Instead, I found a functional hash-map that was approximately four times > slower than Haskell's IntMap. I find this puzzling, and would love to > puzzle it out with you folks. > > First, the test case: > > (ns maptest (:gen-class)) > > (defn mk-random-stream [] > (let [r (new ec.util.MersenneTwisterFast)] > (repeatedly (fn [] (. r (nextInt)))))) > > (defn -main [sn] > (let [n (Integer/parseInt sn) > rs (take (* 2 n) (mk-random-stream))] > (time (let [m (apply hash-map (take (* n 2) (interleave rs rs)))] > (reduce > (fn [s k] (let [v (get m k)] > (+ s (if (nil? v) 0 v)))) > 0 > (take n (drop (/ n 2) rs))))))) > > We generate an n-sized hash tree, and then do n accesses, half of which > match and half of which miss. We compute the sum of all the values that > catch. We see the following characteristics: > > n Clojure Haskell (HAMT) Haskell (IntMap) > 32K .56s .30s .09s > 64K .84s .69s .22s > 128K 1.65s 1.50s .46s > 256K 2.94s 3.23s 1.17s > 512K 7.32s 6.96s 2.70s > > I was careful to compile the Clojure code before attempting to run it. > I also pre-allocate the entire random sequence to prevent it from > muddying the execution time (although I am using Sean Luke's excellent > fast Mersenne Twister [1]). The full string I used to invoke the > program was: > > /usr/lib/jvm/java-6-sun-1.6.0.16/bin/java -Dfile.encoding=UTF-8 \ > -classpath $CLASSES maptest $@ > > The fact that it's similar in performance to the Haskell > reimplementation (I'd say that the variance is not particularly > significant and both are about on par performance wise) seems to > validate the testing methodology, I hope, though the real proof of the > pudding would lie in implementing Haskell-style IntMap in Java. > > You can see the test code for the Haskell versions here: > > http://github.com/ezyang/hamt > > So... what's up with these numbers? Is my methodology wrong? Is the > garbage collector sucking? Is the algorithm just not as good as it > makes out to be? > > Cheers, > Edward > > [1]http://www.cs.gmu.edu/~sean/research/ -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
