A idea nobody has yet suggested—maybe because it's completely wrong.

If your big file is static and contains 100 different fields referring to pin as a key, you can replace it with 100 DBM files, every file containing only pin-field pairs.

Then you can create a big hash containing references to DBM-tied hashes, and get a value for a certain field like $name = $fields{name}{$pin}. As you know which fields you need, you can load only corresponding DBM files.