Is $table a compiled regexp? If it's not, you're compiling regexps over and over again for nothing. In fact, there's no reason to have multiple regexps. 

use Regexp::List qw( );
my $re = Regexp::List->new(modifiers => 'i')
                     ->list2re( map lc($hash{$_}[0]),
                                keys %hash
                              );

# or:
# my ($re) = map qr/$_/i,
#            join '|',
#            map quotemeta(lc($hash{$_}[0])),
#            keys %hash;


while (my $cur_line = <$fh_log>) 
{ 
   while ($cur_line =~ /($re)/g)
   { 
      my $table = lc($1);
      if ($tables{$table}) {
         # Count up how many times this table is referenced. 
         $table_stats{$table}++; 
         $table_refs++;
      } 
   } 
}

[download]

An alternative solution would be to extract the words in $cur_line and look for them in a hash. 

my %tables = map { lc($hash{$_}[0]) => 1 } keys %hash;

while (my $cur_line = <$fh_log>) 
{ 
   while ($cur_line =~ /(\w+)/g)
   { 
      my $table = lc($1);
      if ($tables{$table}) {
         # Count up how many times this table is referenced. 
         $table_stats{$table}++; 
         $table_refs++;
      } 
   } 
}

[download]

I suspect the first method is better.

In reply to Re: Perl Optimization by ikegami
in thread Perl Optimization by Chivalri

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.