Hi all,

Am writing about MCE being one option. 4 million is a big number. Therefore will describe various ways (non-chunking and chunking).

First, chunk_size => 1

   use MCE::Loop max_workers => 4, chunk_size => 1;

   ## non-chunking takes 2m18s to complete

   mce_loop {
      MCE->say($_);

   } 1..4_000_000;
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Next, chunk_size => 'auto'

   use MCE::Loop max_workers => 4, chunk_size => 'auto';

   ## chunking takes 0m12s to complete (IPC becomes 11.5x faster)

   mce_loop {
      my ($mce, $chunk_ref, $chunk_id) = @_;

      my @o; for (@{ $chunk_ref }) {
         push @o, $_;
      }
      MCE->say(@o);

   } 1..4_000_000;
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Finally, processing a file directly containing 4 million rows.

   use MCE::Loop max_workers => 4, chunk_size => 'auto';

   ## processing a file directly (mce_loop_f) takes 0m11.7s

   mce_loop_f {
      my ($mce, $chunk_ref, $chunk_id) = @_;
      chomp @{ $chunk_ref };

      my @o; for (@{ $chunk_ref }) {
         push @o, $_;
      }
      MCE->say(@o);

   } '/path/to/four_million_rows.txt';
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But hold on... Much time comes from writing 4 million rows to STDOUT. Fasten your seatbelt. Rerunning and directing output to /dev/null. The time also includes MCE->say(...)

   ## array non-chunking...:  1m54.467s
   ## array auto-chunking..:  0m 0.843s   136x
   ## file  auto-chunking..:  0m 0.467s   245x
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Running again by commenting out MCE->say(...) to take that out of the equation. Am pleasantly surprised to see 4 million rows with chunk_size 1 in just 1 minute. Gosh, that is fast considering chunk_size => 1 (over 61k per second). However, chunking reduces IPC altogether. Furthermore, MCE can process an input file directly for even lesser overhead.

   ## array non-chunking...:  1m 5.458s
   ## array auto-chunking..:  0m 0.821s    80x
   ## file  auto-chunking..:  0m 0.411s   159x
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It's not fair... :) Part of that time includes the time to load Perl itself and any modules. There is also the time to spawn 4 workers and shutting down in the end. I tested by adding MCE->last. The time needed is 0m0.074s. Therefore, the 0.411s above is really 0.337.

   mce_loop_f {
      MCE->last;    # immediately leaves the block and input
      ... 
   } '/path/to/four_million_rows.txt';
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Well then, here are the times by subtracting 0.074s from above to get the time needed for IPC only. Ha, still not able to break 1 minute for chunk_size => 1.

   ## array non-chunking...:  1m 5.384s
   ## array auto-chunking..:  0m 0.747s    88x
   ## file  auto-chunking..:  0m 0.337s   194x
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Chunking enables IPC to run many times faster due to lesser overhead.