Curious about the HashTable performance issues

Question

I read that hash tables in Haskell had performance issues (on the Haskell-Cafe in 2006 and Flying Frog Consultancy\'s blog in 2009), and since I like Haskell it worried me.<

Answer 1

A question like this can really be settled only by experiment. But if you don't have the time or money to do experiments, you have to ask other people what they think. When you do so, you might want to consider the source and consider whether the information given has been reviewed or vetted in any way.

Jon Harrop has advanced some interesting claims about Haskell. Let me suggest that you search on Google Groups and elsewhere for evidence of Harrop's expertise in Haskell, Lisp, and other functional languages. You could also read the work by Chris Okasaki and Andy Gill on Patricia trees in Haskell, see how their expertise is regarded. You can also find whose claims, if any, have been checked by a third party. Then you can make up your own mind how seriously to take different people's claims about the performance of different functional languages.

Oh, and don't feed the troll.

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P.S. It would be quite reasonable for you to do your own experiments, but perhaps not necessary, since the trusty Don Stewart presents some nice microbenchmarks in his fine answer. Here's an addendum to Don's answer:

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Addendum: Using Don Stewart's code on an AMD Phenom 9850 Black Edition clocked at 2.5GHz with 4GB RAM, in 32-bit mode, with ghc -O,

• With the default heap, the IntMap is 40% faster than the hash table.
• With the 2G heap, the hash table is 40% faster than the IntMap.
• If I go to ten million elements with the default heap, the IntMap is four times faster than the hash table (CPU time) or twice as fast by wall-clock time.

I'm a little surprised by this result, but reassured that functional data structures perform pretty well. And confirmed in my belief that it really pays to benchmark your code under the actual conditions in which it's going to be used.