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

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<chapter>
  <header>
    <copyright>
      <year>2001</year><year>2013</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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      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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      under the License.
    </legalnotice>

    <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, based
    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 only contains the first type of efficient
    code. If that turns out to be too slow, profile the application
    to find out where the performance bottlenecks are and optimize only the
    bottlenecks. Let other code stay as clean as possible.</p>

    <p>Fortunately, compiler and runtime optimizations introduced in
    Erlang/OTP R12B makes it easier to write code that is both clean and
    efficient. For example, 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 teach 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.
    This guide does not include general tips about optimization that
    works in any language, such as moving common calculations out of loops.</p>
  </section>

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