path: root/system/doc/efficiency_guide/introduction.xml

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<chapter>
  <header>
    <copyright>
      <year>2001</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
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    <title>Introduction</title>
    <prepared>Bjorn Gustavsson</prepared>
    <docno></docno>
    <date>2007-11-21</date>
    <rev></rev>
    <file>introduction.xml</file>
  </header>

  <section>
    <title>Purpose</title>

    <quote><p>Premature optimization is the root of all evil. -- D.E. Knuth</p></quote>

    <p>Efficient code can be well-structured and clean code, based on
    on a sound overall architecture and sound algorithms.
    Efficient code can be highly implementation-code that bypasses
    documented interfaces and takes advantage of obscure quirks in
    the current implementation.</p>
    
    <p>Ideally, your code should only contain the first kind of efficient
    code. If that turns out to be too slow, you should profile the application
    to find out where the performance bottlenecks are and optimize only the
    bottlenecks. Other code should stay as clean as possible.</p>

    <p>Fortunately, compiler and run-time optimizations introduced in
    R12B makes it easier to write code that is both clean and
    efficient. For instance, the ugly workarounds needed in R11B and earlier
    releases to get the most speed out of binary pattern matching are
    no longer necessary. In fact, the ugly code is slower
    than the clean code (because the clean code has become faster, not
    because the uglier code has become slower).</p>
    
    <p>This Efficiency Guide cannot really learn you how to write efficient
    code. It can give you a few pointers about what to avoid and what to use,
    and some understanding of how certain language features are implemented.
    We have generally not included general tips about optimization that will
    work in any language, such as moving common calculations out of loops.</p>
  </section>

  <section>
    <title>Prerequisites</title>
    <p>It is assumed that the reader is familiar with the Erlang
      programming language and concepts of OTP.</p>
  </section>
</chapter>