I'm researching some performance problems with one of our Web sites and stumbled across some legacy code that's getting pulled into our system. This code uses $` and $' variables with regular expression matches. From the perlre docs (emphasis mine):

WARNING: Once Perl sees that you need one of "$&", "$`", or "$'" anywhere in the program, it has to provide them for every pattern match. This may substantially slow your program.

In fact, in tests that I've run, it appears that the mere existence of these variables will trigger this behavior, regardless of whether or not the code that accesses them will be executed. Removing these variables seems to consistently get me a ten percent bump in regex performance.

Since mod_perl is a persistent Perl interpreter embedded in the Web server, it seems to me that any reference to these variables will impact all regex matches in a mod_perl environment, regardless of whether or not my code actually uses those variables. Is this the case? I don't know enough about benchmarking snippets in a mod_perl environment to easily verify this.

Cheers,
Ovid

New address of my CGI Course.

In reply to Naughty Regular Expressions and mod_perl by Ovid

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.