for ( 1 ..   111_111 ) { ... }      # 3 * 3,  1 million
   for ( 1 .. 1_111_111 ) { ... }      # 3 * 3, 10 million

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;

use Archive::Zip ();
use File::Copy qw(move);
use File::Find ();
use File::Temp (); $File::Temp::KEEP_ALL = 1;

use Excel::Writer::XLSX;
use MCE::Signal qw($tmp_dir -use_dev_shm);
use MCE::Loop;

my $nodeList = [ [ 'AMS' , 'a' ], [ 'APJ' , 'ap' ], [ 'EMEA', 'e' ] ];
my ($center, $format);

sub init_wb {

   my $wn = shift;

   # Increment $wn by 1 since worksheet xml files begin at 1
   $wn++; mkdir "$tmp_dir/$wn";

   my $wb = Excel::Writer::XLSX->new("$tmp_dir/$wn/tmp.xlsx");

   $wb->set_tempdir("$tmp_dir/$wn");
   $wb->set_optimization();

   # Set workbook properties
   $wb->set_properties(
      title    => 'Node List',
      author   => 'L_WC demo',
      comments => 'Node List',
   );

   # Define/add formats to the workbook
   $center = $wb->add_format(align => 'center');
   $format = $wb->add_format(align => 'center', bg_color => 44);

   # Add worksheets, specify formats for columns/rows
   for (0 .. @{ $nodeList } - 1) {
      $wb->add_worksheet($nodeList->[$_][0]);
      $wb->sheets($_)->set_column(0, 4, 15, $center);
   }

   return $wb;
}

sub merge_wb_data {

   my $wb_file = shift;
   my ($zip, @pths, @xlsx_files) = (Archive::Zip->new());
   local ($@, $!, $^E, $?);

   # Other files, e.g. table data likely need the same and not done
   # for this demonstration. Just worksheet files are merged.
   # I received help by reading _store_workbook inside
   # Excel::Writer::XLSX::Workbook.pm.

   # Find worksheet files 2,3,...
   for my $_num (1 .. @{ $nodeList }) {
      my $wanted = sub {
         push @pths, $1 if $File::Find::name =~ /(.*)\/sheet$_num\.xml/;
      };
      File::Find::find({
         wanted => $wanted, untaint => 1, untaint_pattern => qr|^(.+)$|
      }, "$tmp_dir/$_num");
   }

   # Move worksheet files 2,3,... to where worksheet 1 data resides
   for (0 .. @pths - 1) {
      unlink $pths[$_]."/../../../tmp.xlsx";
      if ($_ > 0) {
         my $_num = $_ + 1; unlink $pths[0]."/sheet$_num.xml";
         move $pths[$_]."/sheet$_num.xml", $pths[0]."/sheet$_num.xml";
      }
   }

   # Re-zip xlsx files
   my $wanted   = sub { push @xlsx_files, $File::Find::name if -f };
   my $temp_dir = $pths[0]."/../../";
   my $short_name;

   File::Find::find({
      wanted => $wanted, untaint => 1, untaint_pattern => qr|^(.+)$|
   }, $temp_dir);

   for my $file_name (@xlsx_files) {
      $short_name =  $file_name;
      $short_name =~ s{^\Q$temp_dir\E/?}{};
      $zip->addFile($file_name, $short_name);
   }

   open my $fh, '>', $wb_file or die "Error opening xlsx file: $!\n";
   binmode $fh; $zip->writeToFileHandle($fh);
   close   $fh;
}

# --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

MCE::Loop::init(
   max_workers => scalar(@{ $nodeList }),
   chunk_size => 1, use_threads => 0,
);

mce_loop {
   my ($region, $sql) = ($_->[0], $_->[1]);
   my ($wb, $ws);

   # Acquire data from the DB. Each worker must obtain a handle.
   # The DB logic is similar to running serially. Just the where
   # clause is likely unique for each region.


   # Fill worksheet rows/cells
   if ($region eq 'AMS') {
      $wb = init_wb(0); $ws = $wb->sheets(0);
      $ws->write(0, 2, 'foo', $format);
      for ( 1 .. 111_111 ) {
         $ws->write($_, 0, 1000 + $_);
         $ws->write($_, 2, 2000 + $_);
         $ws->write($_, 4, 3000 + $_);
      }
      print "AMS  ---- DONE.\n";
   }
   elsif ($region eq 'APJ') {
      $wb = init_wb(1); $ws = $wb->sheets(1);
      $ws->write(0, 2, 'bar', $format);
      for ( 1 .. 111_111 ) {
         $ws->write($_, 0, 4000 + $_);
         $ws->write($_, 2, 5000 + $_);
         $ws->write($_, 4, 6000 + $_);
      }
      print "APJ  ---- DONE.\n";
   }
   elsif ($region eq 'EMEA') {
      $wb = init_wb(2); $ws = $wb->sheets(2);
      $ws->write(0, 2, 'baz', $format);
      for ( 1 .. 111_111 ) {
         $ws->write($_, 0, 7000 + $_);
         $ws->write($_, 2, 8000 + $_);
         $ws->write($_, 4, 9000 + $_);
      }
      print "EMEA ---- DONE.\n";
   }

   $wb->close() if $wb;

} $nodeList;

# Shutdown MCE
MCE::Loop::finish();

# Merge data into one workbook
merge_wb_data('Node_List.xlsx');

print "Node List is Done.\n";