While trying to post a snippet that would demonstrate the doubling of the buffer size, I found that I can only account for an addition of at most 3 bytes more than needed. 

use Devel::Size qw( size );

my $s = '';
for (0..1024*1024) {
   printf("%2d %3d\n", length($s), size($s));
   $s .= 'a';
}

[download]
...
1048563 1048588
1048564 1048592
1048565 1048592
1048566 1048592
1048567 1048592
1048568 1048596
1048569 1048596
1048570 1048596
1048571 1048596
1048572 1048600
1048573 1048600
1048574 1048600
1048575 1048600
1048576 1048604

[download]

It allocates the nearest divisible by 4 amount.
Similar results when appending more than one byte.
Devel::Peek concurs.
ActivePerl 5.8.8 on WinXP.

In reply to Re^4: Is there something faster than string concatenation? (hermit crabs) by ikegami
in thread Is there something faster than string concatenation? by rdj

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