Simple addition results in warnings "Argument isn't numeric" whenever an empty string is there for a field that is nevertheless numeric.

And your code warns for the string "abc" in a numeric field. You didn't perform validation, so neither did I.

savings from converting Unix time from 10-character strings to 4-byte integers are significant.

A measly 16% savings.

$ perl -MDevel::Size=total_size -E'my @a; for (1..3000*6000/10) { my $
+item = "1234567890"; push @a, $item; } say(total_size(\@a))'
87588692

$ perl -MDevel::Size=total_size -E'my @a; for (1..3000*6000/10) { my $
+item = "1234567890"; $item = 0+$item; push @a, $item; } say(total_siz
+e(\@a))'
73188692
[download]

Anyway, the question was how to make array processing faster

So why are you complaining about a little extra memory.

You missed the point. I have no complaints about memory used, I have complaints about space taken by array frozen with Storable. Or rather, pushed to a socket with nstore(). My tests show ~50% reduction in size on actual data written to disk file against unprocessed text file, which is not so measly IMHO; considering that the data comes in bursts every three seconds or so, having its size reduced twice goes as significant in my book.

Anyway, the question was: how do I make array processing go faster than does my code above?

Regards,
Alex.

Wait, what? You are unpacking data just to turn around and re-pack it with nstore? It would go way faster if you did the unpacking on the other side of the socket. You wouldn't even have to use nstore.