Results are in for 60 million cells. Each worker writes 1 million rows x 20 columns wide. Total 60 million cells.

   # Change line 44 inside init_wb
   $wb->sheets($_)->set_column(0, 4, 15, $center);

   # To this
   $wb->sheets($_)->set_column(0, 19, 15, $center);
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   # Replace the if/elsif block inside mce_loop with the following

   # Fill worksheet rows/cells
   if ($region eq 'AMS') {
      $wb = init_wb(0); $ws = $wb->sheets(0);
      $ws->write(0, 2, 'foo', $format);
      for my $row (1..1e6) { for my $cell (0..19) {
         $ws->write($row, $cell, $row + $cell + 10e6);
      }}
      print "AMS  ---- DONE.\n";
   }
   elsif ($region eq 'APJ') {
      $wb = init_wb(1); $ws = $wb->sheets(1);
      $ws->write(0, 2, 'bar', $format);
      for my $row (1..1e6) { for my $cell (0..19) {
         $ws->write($row, $cell, $row + $cell + 20e6);
      }}
      print "APJ  ---- DONE.\n";
   }
   elsif ($region eq 'EMEA') {
      $wb = init_wb(2); $ws = $wb->sheets(2);
      $ws->write(0, 2, 'baz', $format);
      for my $row (1..1e6) { for my $cell (0..19) {
         $ws->write($row, $cell, $row + $cell + 30e6);
      }}
      print "EMEA ---- DONE.\n";
   }
[download]

It takes 4 and 1/2 minutes to write 60 million cells. Opening in LibreOffice takes 4 minutes and 22 seconds before the data appears. LibreOffice consumes 1 GB of memory at that point.

$ time perl write_60mil.pl
AMS  ---- DONE.
EMEA ---- DONE.
APJ  ---- DONE.
Node List is Done.

real   4m35.239s
user  12m 3.641s
sys    0m 4.242s
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I watched the system while running. The /dev/shm requires minimum 5 GB (consumed 4.8 GB). The workers themselves each consume 21 MB of memory. The final xlsx file is 200 MB. In other words, this will run on a Linux system or VM having 6 GB of memory. I resized /dev/shm as follow before running.

# update /etc/fstab
tmpfs /dev/shm tmpfs defaults,size=5g 0 0

# afterwards, remount /dev/shm
mount -o remount /dev/shm
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This has been rather interesting and enjoyed trying. The write_60mil.pl script breaks 200k cells per second (218k).

Kind regards, Mario