It appears to me (perhaps wrongly so) that the problem reduces down to how to print all keys of a hash without Perl making a new list of all keys of that hash in order for the print to work? Assumption is that doubling the size of the storage for key values will exceed physical memory.

In a more general sense: how to call a sub for each hash entry as the hash table is traversed.

If that can be done, then output all keys to a file (call a print routine for each entry). Call a system sort routine for that file. The Perl program may be paged out. Many files may be created and lots of memory may be consumed, but when that sort finishes, there is a file that is in hash key order and all the physical memory that system sort used is now free.

Perl program reads that big file (millions of lines) and assigns sequential numbers to each entry.

Why wouldn't that work?

In reply to Re^3: In-place sort with order assignment by Marshall
in thread In-place sort with order assignment by BrowserUk

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