Hello,

I recently ran Benchmark on some of my code and am curious as to how best to look at the results.

In the follwing code $link is an object which can be loaded from the database or the cache using the two private functions benchmarked and $criteria is a hashhref.

use Benchmark qw(cmpthese);

cmpthese( 10_000,
    {
      'From Cache' => sub{ $link->_load_from_database( $criteria ); },
      ' From DBI' => sub{ $link->_load_from_cache ( $criteria ); }
    }
  );

Update: 

use Benchmark qw(cmpthese);

cmpthese( 10_000,
      {
       'From Cache' => sub{ $link->_load_from_cache   ( $criteria ); }
+,
       '  From DBI' => sub{ $link->_load_from_database( $criteria ); }
      }
    );

[download]
The results of the benchmarking are: 
Benchmark: timing 10000 iterations of   From DBI, From Cache...
  From DBI: 16 wallclock secs (13.66 usr +  1.50 sys = 15.16 CPU) @ 65
+9.63/s (n=10000)
From Cache: 16 wallclock secs ( 6.86 usr +  0.75 sys =  7.61 CPU) @ 13
+14.06/s (n=10000)
             Rate   From DBI From Cache
  From DBI  660/s         --       -50%
From Cache 1314/s        99%         --

[download]
As you can see the Cache code is much faster at 1314/sec (DBI is 660/sec). However the wall clock times for both are the same, and as 10_000 iterations were timed this would imply that in user time there is not much to choose between them.

My question is "how should I look at these results?". What generally accounts for time that Benchmark does not see, and which time result should I use in making performance questions. I hope that this is enough detail for a general discussion as opposed to specifically looking at the code I posted. 

--
tidiness is the memory loss of environmental mnemonics

[download]

Update per author - dvergin 2003-02-12

In reply to Interpreting Benchmark results. by EvdB

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