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FAQ 3.18 How can I free an array or hash so my program shrinks?

 
 
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      03-14-2011
This is an excerpt from the latest version perlfaq3.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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3.18: How can I free an array or hash so my program shrinks?

(contributed by Michael Carman)

You usually can't. Memory allocated to lexicals (i.e. my() variables)
cannot be reclaimed or reused even if they go out of scope. It is
reserved in case the variables come back into scope. Memory allocated to
global variables can be reused (within your program) by using undef()
and/or delete().

On most operating systems, memory allocated to a program can never be
returned to the system. That's why long-running programs sometimes re-
exec themselves. Some operating systems (notably, systems that use
mmap(2) for allocating large chunks of memory) can reclaim memory that
is no longer used, but on such systems, perl must be configured and
compiled to use the OS's malloc, not perl's.

In general, memory allocation and de-allocation isn't something you can
or should be worrying about much in Perl.

See also "How can I make my Perl program take less memory?"



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are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
perlfaq.pod.
 
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