[Haskell-cafe] is 256M RAM insufficient for a 20 million element Int/Int map?

Philippa Cowderoy flippa at flippac.org
Sun Oct 19 07:58:35 EDT 2008

On Sun, 19 Oct 2008, Bulat Ziganshin wrote:

> Hello Philippa,
> Sunday, October 19, 2008, 3:25:26 PM, you wrote:
> >> ... that, like everything else, should be multiplied by 2-3 to
> >> account GC effect
> > Unless I'm much mistaken, that isn't the case when you're looking at the
> > minimum heap size because the GC'll run more frequently when you hit the
> > max heap size supported anyway, no?
> what you mean? max heap size is 2gb probably. it may be configured on
> cmdline and if you will enable say 200 mb heap and your program use
> only 180 mb - it will run successfully, using only 200 mb of memory.
> drawback, of course, is that it may become 10x slower

Ah, so you can't trust GHC to pick a max heap size within what the OS 
actually has available? That does make the RTS option rather necessary. 
But well worth knowing if you're trying to make something run in a known 

flippa at flippac.org

The task of the academic is not to scale great
intellectual mountains, but to flatten them.

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