gistfile1.rb

def sql
  /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/
end
def sql_frozen
  /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/.freeze
end
SQLo      = /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/o
SQL       = /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/
SQLFrozen = /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/.freeze

require 'rubygems'
require 'benchmark/ips'

STATEMENT = "SELECT * FROM card_payments"

Benchmark.ips do |x|
  x.config(:time => 45, :warmup => 2)

  x.report "inline /o" do
    STATEMENT =~ /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/o
  end
  x.report "inline" do
    STATEMENT =~ /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/
  end
  x.report "inline [frozen]" do
    STATEMENT =~ /\A\s*(SELECT|INSERT|UPDATE|DELETE).*(FROM|JOIN)\s*`?(my_interesting|tables)`?/.freeze
  end
  x.report "method" do
    STATEMENT =~ sql
  end
  x.report "method [frozen]" do
    STATEMENT =~ sql_frozen
  end
  x.report "constant /o" do
    STATEMENT =~ SQLo
  end
  x.report "constant" do
    STATEMENT =~ SQL
  end
  x.report "constant [frozen]" do
    STATEMENT =~ SQLFrozen
  end
end

__END__
Calculating -------------------------------------
           inline /o    51.435k i/100ms
              inline    52.298k i/100ms
     inline [frozen]    50.497k i/100ms
              method    48.986k i/100ms
     method [frozen]    45.558k i/100ms
         constant /o    52.396k i/100ms
            constant    49.258k i/100ms
   constant [frozen]    52.501k i/100ms
-------------------------------------------------
           inline /o    815.788k (± 9.8%) i/s -     36.262M
              inline    818.869k (± 9.7%) i/s -     36.399M
     inline [frozen]    761.042k (±11.6%) i/s -     33.631M
              method    791.291k (± 6.4%) i/s -     35.466M
     method [frozen]    694.295k (±17.6%) i/s -     29.977M
         constant /o    751.494k (±13.6%) i/s -     33.009M
            constant    746.568k (±12.2%) i/s -     33.003M
   constant [frozen]    757.508k (±12.3%) i/s -     33.443M

You should try the once flag, /…/o also.