I am looking at a possible "time/space" trade-off problem. I am evaluating storing a set of data that is keyed by 3 attributes:

attr1 is a number in the range 200-35000
attr2 is a string, 6-9 characters
attr3 is a string of 10 characters

The hash key is "attr1.attr2.attr3", The hash content is a ref to an anon array.

Could there be a significant performance improvement by maintaining a second hash of just 'attr1' to pre-determine if any keys start with attr1? 

   my $arrayRef;
   if ( defined ?attr1Hash{$attr1}){
      my $key ="attr1.attr2.attr3";
      $arrayRef = $fullHash{$key};
   } 
   if ( defined $arrayRef){
      ...
   }

[download]
vs 
   my $arrayRef;
   my $key ="attr1.attr2.attr3";
   $arrayRef = $fullHash{$key};
   if ( defined $arrayRef){
      ...
   }

[download]
UPDATE:

I have a process that is watching (ala 'less') the system syslog file for pre-determined message keywords, which are reported across the net to a higher authority. Some of the tests done on a record may cause sub-shells to be spawned to determine system state.
But basicly pretty straight forward.

Enhancement creep:

Generate a special event report if any unique process(pid), in a specified time period, creates more than 3 of the syslog messages. I have gone from statless scan to a time limited historic context.

The module I am working on holds the 'state' 

    $EventHash{$pid} = [ create_ts, last_upt, $ev_cnt];

[download]

It is always better to have seen your target for yourself, rather than depend upon someone else's description.

In reply to Hash space/ time tradeoff by Wiggins

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