Haskell's hash tables revisited: part 2

Our previous blog post contained several benchmark results comparing the new GHC 6.12.3 with F#. We have since discovered some other points of interest regarding this benchmark.

Firstly, the results for Haskell rely on the use of a garbage collector that prevents parallelism. If the more modern multicore-friendly GC is used (by compiling with -threaded and running with +RTS -N8) then the time taken increases from 4.5s to 10.6s. This is over 2× slower than before and now over 13× slower than F#. Naturally, the F# was already using the multicore-capable .NET garbage collector so this was an unfair bias in favor of Haskell.

Secondly, the Haskell code exploits an algorithmic optimization on the assumption that the keys are unique. This is often not the case in practice and, again, the F# code did not exploit such an assumption so this was another unfair bias in favor of Haskell. A fairer comparison may be obtained by changing from the insert function to the update function in the Haskell code. Again, this incurs a substantial performance penalty and increases the time taken to 20.6.

With these alterations, Haskell becomes 26× slower than F# on this benchmark even with the latest GHC. Although these latest improvements are a step in the right direction, it seems that Haskell still has a long way to go before attaining competitive performance with mutable data structures.

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