$ perl pm_hash_clear_vs_undef_1214851.pl
Checking container differences between delete and clear:
Hash size (initial): 0/8
Hash size (after fill): 62/64
Hash size (after clear): 0/64
Hash size (after delete): 0/8

             Rate    delete     reuse overwrite
delete    38049/s        --       -3%      -39%
reuse     39358/s        3%        --      -37%
overwrite 62375/s       64%       58%        --