[Haskell-cafe] cereal vs. binary

wren ng thornton wren at freegeek.org
Tue Jul 6 03:18:18 EDT 2010

braver wrote:
> I dump results of a computation as a Data.Trie of [(Int,Float)].  It
> contains about 5 million entries, with the lists of 35 or less pairs
> each.  It takes 8 minutes to load with Data.Binary and lookup a single
> key.  What can take so long?  If I change from compressed to
> uncompressed (and then decode), it's the same time...  It's not IO,
> CPU is loaded 100%.

The Binary instance for Trie is based on the old Binary instance for 
Data.IntMap. There were some corner-case performance issues with the 
latter which were recently fixed[1], but I haven't had a chance to look 
at the new instance or to figure out if the changes would also be 
relevant for Trie. So this might be a potential source of your problems.

[1] Alas, I can't find the thread discussing the new instance ATM.

> I'm now thinking of using cereal.  Given I have Data.Binary in place,
> what needs to be changed to work with cereal?  Is it binary-
> compatible?  How can one construct a cereal instance for Data.Trie?

If you send me an instance, I can apply the patch.

Live well,

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