Because the second structure uses more memory (to build if not when complete) than the first.

Not so!

The AoH with 50 hashes each with 250_000 key/value pairs requires close to 1 GB, when finished and over 1.5GB to construct. Whereas the array of 10e6 integers requires just 220MB, and a peak of 330MB to construct.

The problem is that none of the memory freed up by releasing the AoH is large enough to be reused for the AV for the array, because Perl doesn't defragment or coalese freed memory. So, even though Perl has gobs of free space available to it, it has to go back to the OS for more in order to get big enough chunks for the array.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

In reply to Re^2: out of memory problem after undef by BrowserUk
in thread out of memory problem after undef by sduser81

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