The foreach loop is very slow (takes 2 days to run) because there are 31,197 alarms each analyzing 155 Quench Times. I wrote sub GetQuenchInfo to create a hash to try to speed up...

You made two mistakes here: First, you started optimizing within a loop before you considered what you could move out of the loop. Second, you began pursuing a particular optimization (creating a hash) before you'd gathered data on where your script was spending its time.

Making a database connection and running the queries can be moved out of the loop, since nothing they do depends on $supply, which is the only thing varying in that loop. (Is this intentional, or a bug?) But for a moment, let's pretent they can't be moved out of the loop.

Since you know the performance problem is in the loop, a reasonable approach is to pick the loop apart, looking for where the script might be spending time. Then add some simple timing code to gather data. For example:

  my $aboutToConnect = time();  # start timing
  my $dbEvents = new Sybase::CTlib 'harmless','harmless','OPSYB1','fil
+leventsT';
  print "Sybase::CTlib took ", time() - $aboutToConnect,
        " seconds to connect\n";
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You might then have discovered that making a new database connection is relatively expensive.

Ditto for timing the queries.

If you discover that 99% of your time is going to database work, then trying to improve performance by using a hash is pointless, unless reducing that 1% to 0.5% is going to pay off.