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


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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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