...is it better to open the output file once, in the beginning and keep it open ..., or open and close it whenever I have something to print into it?

Opening is a system call. Closing results in system calls. Both of these acts consume some amount of time greater than zero. The significance of the amount of time each call takes is something that one could only quantify by knowing how many times the open/close cycle are happening in your script, and how much time your script is spent inside of these calls.

This important information that reveals the significance of the open/close calls within your runtime can be determined by using Devel::NYTProf. But if your script is taking 15 minutes to run with your data set, before using NYTProf, create a sample data set that's about 10-20% of that size while remaining representative of your real data. Then profile, and see where your problems are.


Dave

In reply to Re: Tip on better performance: Open and close output file or leave it open? by davido
in thread Tip on better performance: Open and close output file or leave it open? by Anonymous Monk

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.