My impression is that Judy arrays are about addressing speed rather than space concerns with an emphasis on cache coherency as an optimisation technique. Probably not really applicable in a Perl context.

I don't have any first hand experience but as I said they claim to be far more memory efficient.

Of course it also depends on the OPs usage, storing 500M Perl arrays holding just two integer entries will still exhaust his memory.

Cheers Rolf
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Wikisyntax for the Monastery}