Yves said that the XS version of Data::Dumper was inefficient because

Yves said that the XS version of Data::Dumper was inefficient because
it keeps triggering realloc() due to sv_cat(). Here's a rather brute
force approach to pre-stretching the buffer - if there are less than
40 bytes free, grow it by 50%.

Surprisingly effective for my test program
./perl -Ilib -MData::Dumper -MStorable=retrieve -we \
    'print Dumper(retrieve(shift))' ~/.cpan/Metadata >/dev/null

Before
real    2m42.921s
user    1m43.321s
sys     0m55.611s

After
real    0m5.205s
user    0m4.885s
sys     0m0.255s

Same 25M of output, byte for byte. :-)

p4raw-id: //depot/perl@28963