perl -e '$k="aaaaa";
 for $i (1..1_000_000)
 { $h1{$k}={foo=>"bar",bar=>"foo",iter=>$i}; $h1{$k}{total}++; $k++}
 sleep 20'
## consumes 344 MB in ~14.4 sec

perl -e '$k="aaaaa";
 for $i (1..1_000_000)
 {$h1{$k}={foo=>"bar",bar=>"foo",iter=>$i}; $h2{$k}++; $k++}
 sleep 20'
## consumes 352 MB in ~15.0 sec

perl -e '$k="aaaaa";
 for $i (1..1_000_000)
 {$h1{$k}={foo=>"bar",bar=>"foo"}; $h2{$k}++; $h3{$k}=$i; $k++}
 sleep 20'
## consumes 360 MB in ~16.5 sec