GHC/Memory Management

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Revision as of 20:42, 23 June 2009 by Bulatz (talk | contribs) (key property of immutable data)

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Haskell computations produces a lot of memory garbage - much more than conventional imperative languages. It's because data are immutable so the only way to store computation result is to create new data. In particular, every iteration of recursive computation creates new data. But GHC is able to efficiently manage garbage collection, so it's not uncommon to produce 1gb of data per second (most part of which will be garbage collected immediately). So, you may be interested to learn how GHC does such good job.

Haskell computation model is very deiiferent from that of conventional mutable languages. Data immutability forces us to produce a lot of temporary data but it also helps to collect this garbage rapidly. The trick is that immutable data NEVER point to yonger values. Indeed, younger value don't yet exists at the time when old value created, so it cannot be pointed to from scratch. And since values are never modified, it neither can be pointer to later. It is the key property of immutable data.