Instead of using merge-sort alone ( as a plain approach ) a hybrid way of using in-memory sorting and merge-sort can be combined and used together.

That's what the post to which you replied already suggested.

Out of the total 'n' number of files, sort only 'm' files in memory

A 100MB file takes up pretty major chunk of memory already. Remember, if the array isn't preallocated to hold enough lines, twice the size of the data is needed.

If I were to re-implement the work in Perl, I'd probably do something equivalent to

  1. cat * | (cd tmp; split --lines=XXX -bytes=YYY - chunk)
    This maximizes memory usage while limiting memory usage.
  2. for f in tmp/chunk* ; do sort $f >$f.sorted ; done
    The sorting would actually be done before writing out the chunk.
  3. Merge file pairs until only one file remains.

Update: I struck out a statement that's probably wrong. There is overhead, but it should be proportional to the number of lines, not number of bytes.

In reply to Re^3: read and sort multiple files by ikegami
in thread read and sort multiple files by newPerlr

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