I was formulating this same response myself, but I'll provide a minor variation, which does pretty much the same, but uses automatic variables instead of temporary placeholder variables:

my %new_data = ();
foreach ( @DATA ) {
  /^(.*?)\t.*$/;
  push @{$new_data{$1}}, $_;
}
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Either case is equally valid in my eyes - I do not know which is faster, the split() or //, so I'll leave that to better souls than mine to answer on.

The important thing I'd like to point out is that the above method - ran as a step before the server loop - effectively reduces your redundancy to two reads - once to populate the hash, and then once for the server-specific loop.