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<img alt="Erlang logo" src="../erlang-logo.png"><br><small><a href="users_guide.html">User's Guide</a><br><a href="../pdf/otp-system-documentation-5.9.3.1.pdf">PDF</a><br><a href="../index.html">Top</a></small><p><strong>Efficiency Guide</strong><br><strong>User's Guide</strong><br><small>Version 5.9.3.1</small></p>
<br><a href="javascript:openAllFlips()">Expand All</a><br><a href="javascript:closeAllFlips()">Contract All</a><p><small><strong>Chapters</strong></small></p>
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<li id="loadscrollpos" title="Introduction" expanded="true">Introduction<ul>
<li><a href="introduction.html">
Top of chapter
</a></li>
<li title="Purpose"><a href="introduction.html#id62954">Purpose</a></li>
<li title="Prerequisites"><a href="introduction.html#id65420">Prerequisites</a></li>
</ul>
</li>
<li id="no" title="The Eight Myths of Erlang Performance" expanded="false">The Eight Myths of Erlang Performance<ul>
<li><a href="myths.html">
Top of chapter
</a></li>
<li title="Myth: Funs are slow"><a href="myths.html#id64448">Myth: Funs are slow</a></li>
<li title="Myth: List comprehensions are slow"><a href="myths.html#id61406">Myth: List comprehensions are slow</a></li>
<li title="Myth: Tail-recursive functions are MUCH faster
than recursive functions"><a href="myths.html#id62291">Myth: Tail-recursive functions are MUCH faster
than recursive functions</a></li>
<li title="Myth: '++' is always bad"><a href="myths.html#id60058">Myth: '++' is always bad</a></li>
<li title="Myth: Strings are slow"><a href="myths.html#id62534">Myth: Strings are slow</a></li>
<li title="Myth: Repairing a Dets file is very slow"><a href="myths.html#id61135">Myth: Repairing a Dets file is very slow</a></li>
<li title="Myth: BEAM is a stack-based byte-code virtual machine (and therefore slow)"><a href="myths.html#id64006">Myth: BEAM is a stack-based byte-code virtual machine (and therefore slow)</a></li>
<li title="Myth: Use '_' to speed up your program when a variable is not used"><a href="myths.html#id64026">Myth: Use '_' to speed up your program when a variable is not used</a></li>
</ul>
</li>
<li id="no" title="Common Caveats" expanded="false">Common Caveats<ul>
<li><a href="commoncaveats.html">
Top of chapter
</a></li>
<li title="The timer module"><a href="commoncaveats.html#id62547">The timer module</a></li>
<li title="list_to_atom/1"><a href="commoncaveats.html#id61885">list_to_atom/1</a></li>
<li title="length/1"><a href="commoncaveats.html#id60806">length/1</a></li>
<li title="setelement/3"><a href="commoncaveats.html#id58300">setelement/3</a></li>
<li title="size/1"><a href="commoncaveats.html#id65402">size/1</a></li>
<li title="split_binary/2"><a href="commoncaveats.html#id60836">split_binary/2</a></li>
<li title="The '--' operator"><a href="commoncaveats.html#id61766">The '--' operator</a></li>
</ul>
</li>
<li id="no" title="Constructing and matching binaries" expanded="false">Constructing and matching binaries<ul>
<li><a href="binaryhandling.html">
Top of chapter
</a></li>
<li title="How binaries are implemented"><a href="binaryhandling.html#id62932">How binaries are implemented</a></li>
<li title="Constructing binaries"><a href="binaryhandling.html#id66066">Constructing binaries</a></li>
<li title="Matching binaries"><a href="binaryhandling.html#id63610">Matching binaries</a></li>
</ul>
</li>
<li id="no" title="List handling" expanded="false">List handling<ul>
<li><a href="listHandling.html">
Top of chapter
</a></li>
<li title="Creating a list"><a href="listHandling.html#id66709">Creating a list</a></li>
<li title="List comprehensions"><a href="listHandling.html#id66805">List comprehensions</a></li>
<li title="Deep and flat lists"><a href="listHandling.html#id66875">Deep and flat lists</a></li>
<li title="Why you should not worry about recursive lists functions"><a href="listHandling.html#id67017">Why you should not worry about recursive lists functions</a></li>
</ul>
</li>
<li id="no" title="Functions" expanded="false">Functions<ul>
<li><a href="functions.html">
Top of chapter
</a></li>
<li title="Pattern matching"><a href="functions.html#id67142">Pattern matching</a></li>
<li title="Function Calls "><a href="functions.html#id67362">Function Calls </a></li>
<li title="Memory usage in recursion"><a href="functions.html#id67506">Memory usage in recursion</a></li>
</ul>
</li>
<li id="no" title="Tables and databases" expanded="false">Tables and databases<ul>
<li><a href="tablesDatabases.html">
Top of chapter
</a></li>
<li title="Ets, Dets and Mnesia"><a href="tablesDatabases.html#id67596">Ets, Dets and Mnesia</a></li>
<li title="Ets specific"><a href="tablesDatabases.html#id67983">Ets specific</a></li>
<li title="Mnesia specific"><a href="tablesDatabases.html#id68087">Mnesia specific</a></li>
</ul>
</li>
<li id="no" title="Processes" expanded="false">Processes<ul>
<li><a href="processes.html">
Top of chapter
</a></li>
<li title="Creation of an Erlang process"><a href="processes.html#id68191">Creation of an Erlang process</a></li>
<li title="Process messages"><a href="processes.html#id68339">Process messages</a></li>
<li title="The SMP emulator"><a href="processes.html#id68531">The SMP emulator</a></li>
</ul>
</li>
<li id="no" title="Drivers" expanded="false">Drivers<ul>
<li><a href="drivers.html">
Top of chapter
</a></li>
<li title="Drivers and concurrency"><a href="drivers.html#id68634">Drivers and concurrency</a></li>
<li title="Avoiding copying of binaries when calling a driver"><a href="drivers.html#id68675">Avoiding copying of binaries when calling a driver</a></li>
<li title="Returning small binaries from a driver"><a href="drivers.html#id68743">Returning small binaries from a driver</a></li>
<li title="Returning big binaries without copying from a driver"><a href="drivers.html#id68777">Returning big binaries without copying from a driver</a></li>
</ul>
</li>
<li id="no" title="Advanced" expanded="false">Advanced<ul>
<li><a href="advanced.html">
Top of chapter
</a></li>
<li title="Memory"><a href="advanced.html#id68919">Memory</a></li>
<li title="System limits"><a href="advanced.html#id69276">System limits</a></li>
</ul>
</li>
<li id="no" title="Profiling" expanded="false">Profiling<ul>
<li><a href="profiling.html">
Top of chapter
</a></li>
<li title="Do not guess about performance - profile"><a href="profiling.html#id69579">Do not guess about performance - profile</a></li>
<li title="Big systems"><a href="profiling.html#id69661">Big systems</a></li>
<li title="What to look for"><a href="profiling.html#id69681">What to look for</a></li>
<li title="Tools"><a href="profiling.html#id69738">Tools</a></li>
<li title="Benchmarking"><a href="profiling.html#id70245">Benchmarking</a></li>
</ul>
</li>
</ul>
</div></div>
<div id="content">
<div class="innertube">
<h1>1 Introduction</h1>
<h3><a name="id62954">1.1
Purpose</a></h3>
<p>Premature optimization is the root of all evil. -- D.E. Knuth</p>
<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>
<h3><a name="id65420">1.2
Prerequisites</a></h3>
<p>It is assumed that the reader is familiar with the Erlang
programming language and concepts of OTP.</p>
</div>
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