I think that a fetchall_arrayref is very memory intensive and not a good idea.

I guess that DBI or the underlying drives either batch operations automatically, or have options to do so, or don't do it because it's not efficient. Either way I don't think that your "manual" caching will do very much good.

Also you're using ->bind_columns(\$number, \$id,\$start_dat,\$end_dat); which means that after each ->fetch() the variables $number, $id etc have the new values. This is efficient, but only if you use ->fetch(), not ->fetchall_arrayref (which duplicates the work).