If you need 1.4GB to sort 400MB that means that you are probably converting numbers to strings inside the sort.

Yep! That's the problem.

{ ($c, $d) = ($a,$b); $c cmp $d

I wonder if that optimisation could be worked into the internal sort?

I started to suggest that if both had the (same) IOK or NOK flags set, then use a numeric comparison, but I guess it would only take one string embeded at the wrong place for the entire sort to have to be done over.

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In reply to Re^6: Howto Avoid Memory Problem in List::MoreUtils by BrowserUk
in thread Howto Avoid Memory Problem in List::MoreUtils by Anonymous Monk

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