You may find the subthread staring at Re: Index a file with pack for fast access of interest.

The indexing mechanism discussed there isn't directly applicable to your requirements -- it indexes by line number rather than content -- but it should be adaptable to them.

Assuming your sample data is representative -- ie. average record length 47 -- then 30GB represents ~700 million records. And assuming the key numbers are representative, you'd need a 32-bit int to represent those and a 64-bit int to represent the file offset. Hence your index could be built using:

open IN, '<', '/path/to/the/Datafile.txt' or die $!;
open out, '>:raw', /path/to/the/indexfile.idx' or die $!;

my $pos = 0;
print( OUT pack 'VQ', m[^(\d+),], $pos ), $pos = tell( IN ) while <IN>
+;

close OUT;
close IN;
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The output file, with 12 bytes per record would be ~7.6GB.

As the keys in your file appear to be out of order, you would then need to (binary) sort that file.

Once sorted, a binary search would take an average of 30 seeks&reads to locate the appropriate 12-byte index record and another seek&read to get the data record.

If you have a sufficiently well-spec'd machine with (say) 8GB or more of ram, you could load the entire index into memory -- as a single big string and access as a ramfile -- which would probably reduce your lookup time by much more than an order of magnitude.