Tim Bunce's excellent Profiling Memory Usage talk gives some insight into what's going on at the 09:20 minute mark:

sub foo {
   my $var = "X" x 10_000_000;
}
foo();
[download]

Tim explains that:

1. The buffer for the $var lexical is preserved (for next time you call the subroutine).
2. The compiler says hey "X" is a constant and 10_000_000 is a constant, so I'm gonna build you a 10 MB constant! And I'm going to keep it here to one side so when you call this subroutine again I can just copy it in for you! (aka Constant folding).

With recursion, things get much worse (sorry, I couldn't bring myself to watch that part :).

Though Tim's Devel::SizeMe module might be useful, AFAIK it is up for adoption and not being actively developed ATM.

I also keep a list of Memory Tools References (from this list, Mini-Tutorial: Perl's Memory Management by ikegami is definitely worth reading).

OK this makes sense.

Perl can't know beforehand, how often this line is executed.

Even if it cared to check that it's not inside a loop or sub.

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}

In general an assign should COW, but the rules are complex. It's not happening in this case. It's probably a bug.

Dave.

Maybe the string is different in memory depending on when it is created? Unicode vs ASCII or something?

nope, I think eyepops explanation is spot on.

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}