A database, such as SQLite (which requires no "server" – it's all on your local disk) excels at the on-disk operations such as are needed here. You can't "keep all the data in memory," and when you try, the operating system's swap-file becomes a very inefficient backing disk: you aren't really doing the work "in memory" at all. With SQLite, e.g., you can load the data into a table, index the table if it helps, sort the rows, and so on. All of which is done on your local disk. "Don't 'diddle' your code to make it faster – find a better algorithm."

In reply to Re^3: efficient perl code to count, rank by Anonymous Monk
in thread efficient perl code to count, rank by Perl_Noob2021

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