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index.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="generator" content="AsciiDoc 8.6.9">
<title>The Erlang Runtime System</title>
<style type="text/css">
/* Shared CSS for AsciiDoc xhtml11 and html5 backends */
/* Default font. */
body {
font-family: Georgia,serif;
}
/* Title font. */
h1, h2, h3, h4, h5, h6,
div.title, caption.title,
thead, p.table.header,
#toctitle,
#author, #revnumber, #revdate, #revremark,
#footer {
font-family: Arial,Helvetica,sans-serif;
}
body {
margin: 1em 5% 1em 5%;
}
a {
color: blue;
text-decoration: underline;
}
a:visited {
color: fuchsia;
}
em {
font-style: italic;
color: navy;
}
strong {
font-weight: bold;
color: #083194;
}
h1, h2, h3, h4, h5, h6 {
color: #527bbd;
margin-top: 1.2em;
margin-bottom: 0.5em;
line-height: 1.3;
}
h1, h2, h3 {
border-bottom: 2px solid silver;
}
h2 {
padding-top: 0.5em;
}
h3 {
float: left;
}
h3 + * {
clear: left;
}
h5 {
font-size: 1.0em;
}
div.sectionbody {
margin-left: 0;
}
hr {
border: 1px solid silver;
}
p {
margin-top: 0.5em;
margin-bottom: 0.5em;
}
ul, ol, li > p {
margin-top: 0;
}
ul > li { color: #aaa; }
ul > li > * { color: black; }
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font-family: "Courier New", Courier, monospace;
font-size: inherit;
color: navy;
padding: 0;
margin: 0;
}
pre {
white-space: pre-wrap;
}
#author {
color: #527bbd;
font-weight: bold;
font-size: 1.1em;
}
#email {
}
#revnumber, #revdate, #revremark {
}
#footer {
font-size: small;
border-top: 2px solid silver;
padding-top: 0.5em;
margin-top: 4.0em;
}
#footer-text {
float: left;
padding-bottom: 0.5em;
}
#footer-badges {
float: right;
padding-bottom: 0.5em;
}
#preamble {
margin-top: 1.5em;
margin-bottom: 1.5em;
}
div.imageblock, div.exampleblock, div.verseblock,
div.quoteblock, div.literalblock, div.listingblock, div.sidebarblock,
div.admonitionblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.admonitionblock {
margin-top: 2.0em;
margin-bottom: 2.0em;
margin-right: 10%;
color: #606060;
}
div.content { /* Block element content. */
padding: 0;
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/* Block element titles. */
div.title, caption.title {
color: #527bbd;
font-weight: bold;
text-align: left;
margin-top: 1.0em;
margin-bottom: 0.5em;
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div.title + * {
margin-top: 0;
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td div.title:first-child {
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div.content div.title:first-child {
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div.content + div.title {
margin-top: 0.0em;
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div.sidebarblock > div.content {
background: #ffffee;
border: 1px solid #dddddd;
border-left: 4px solid #f0f0f0;
padding: 0.5em;
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div.listingblock > div.content {
border: 1px solid #dddddd;
border-left: 5px solid #f0f0f0;
background: #f8f8f8;
padding: 0.5em;
}
div.quoteblock, div.verseblock {
padding-left: 1.0em;
margin-left: 1.0em;
margin-right: 10%;
border-left: 5px solid #f0f0f0;
color: #888;
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div.quoteblock > div.attribution {
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text-align: right;
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div.verseblock > pre.content {
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font-size: inherit;
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div.verseblock > div.attribution {
padding-top: 0.75em;
text-align: left;
}
/* DEPRECATED: Pre version 8.2.7 verse style literal block. */
div.verseblock + div.attribution {
text-align: left;
}
div.admonitionblock .icon {
vertical-align: top;
font-size: 1.1em;
font-weight: bold;
text-decoration: underline;
color: #527bbd;
padding-right: 0.5em;
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div.admonitionblock td.content {
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border-left: 3px solid #dddddd;
}
div.exampleblock > div.content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
div.imageblock div.content { padding-left: 0; }
span.image img { border-style: none; vertical-align: text-bottom; }
a.image:visited { color: white; }
dl {
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margin-bottom: 0.8em;
}
dt {
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margin-bottom: 0;
font-style: normal;
color: navy;
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dd > *:first-child {
margin-top: 0.1em;
}
ul, ol {
list-style-position: outside;
}
ol.arabic {
list-style-type: decimal;
}
ol.loweralpha {
list-style-type: lower-alpha;
}
ol.upperalpha {
list-style-type: upper-alpha;
}
ol.lowerroman {
list-style-type: lower-roman;
}
ol.upperroman {
list-style-type: upper-roman;
}
div.compact ul, div.compact ol,
div.compact p, div.compact p,
div.compact div, div.compact div {
margin-top: 0.1em;
margin-bottom: 0.1em;
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tfoot {
font-weight: bold;
}
td > div.verse {
white-space: pre;
}
div.hdlist {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
div.hdlist tr {
padding-bottom: 15px;
}
dt.hdlist1.strong, td.hdlist1.strong {
font-weight: bold;
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td.hdlist1 {
vertical-align: top;
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padding-right: 0.8em;
color: navy;
}
td.hdlist2 {
vertical-align: top;
}
div.hdlist.compact tr {
margin: 0;
padding-bottom: 0;
}
.comment {
background: yellow;
}
.footnote, .footnoteref {
font-size: 0.8em;
}
span.footnote, span.footnoteref {
vertical-align: super;
}
#footnotes {
margin: 20px 0 20px 0;
padding: 7px 0 0 0;
}
#footnotes div.footnote {
margin: 0 0 5px 0;
}
#footnotes hr {
border: none;
border-top: 1px solid silver;
height: 1px;
text-align: left;
margin-left: 0;
width: 20%;
min-width: 100px;
}
div.colist td {
padding-right: 0.5em;
padding-bottom: 0.3em;
vertical-align: top;
}
div.colist td img {
margin-top: 0.3em;
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@media print {
#footer-badges { display: none; }
}
#toc {
margin-bottom: 2.5em;
}
#toctitle {
color: #527bbd;
font-size: 1.1em;
font-weight: bold;
margin-top: 1.0em;
margin-bottom: 0.1em;
}
div.toclevel0, div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
margin-top: 0;
margin-bottom: 0;
}
div.toclevel2 {
margin-left: 2em;
font-size: 0.9em;
}
div.toclevel3 {
margin-left: 4em;
font-size: 0.9em;
}
div.toclevel4 {
margin-left: 6em;
font-size: 0.9em;
}
span.aqua { color: aqua; }
span.black { color: black; }
span.blue { color: blue; }
span.fuchsia { color: fuchsia; }
span.gray { color: gray; }
span.green { color: green; }
span.lime { color: lime; }
span.maroon { color: maroon; }
span.navy { color: navy; }
span.olive { color: olive; }
span.purple { color: purple; }
span.red { color: red; }
span.silver { color: silver; }
span.teal { color: teal; }
span.white { color: white; }
span.yellow { color: yellow; }
span.aqua-background { background: aqua; }
span.black-background { background: black; }
span.blue-background { background: blue; }
span.fuchsia-background { background: fuchsia; }
span.gray-background { background: gray; }
span.green-background { background: green; }
span.lime-background { background: lime; }
span.maroon-background { background: maroon; }
span.navy-background { background: navy; }
span.olive-background { background: olive; }
span.purple-background { background: purple; }
span.red-background { background: red; }
span.silver-background { background: silver; }
span.teal-background { background: teal; }
span.white-background { background: white; }
span.yellow-background { background: yellow; }
span.big { font-size: 2em; }
span.small { font-size: 0.6em; }
span.underline { text-decoration: underline; }
span.overline { text-decoration: overline; }
span.line-through { text-decoration: line-through; }
div.unbreakable { page-break-inside: avoid; }
/*
* xhtml11 specific
*
* */
div.tableblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.tableblock > table {
border: 3px solid #527bbd;
}
thead, p.table.header {
font-weight: bold;
color: #527bbd;
}
p.table {
margin-top: 0;
}
/* Because the table frame attribute is overriden by CSS in most browsers. */
div.tableblock > table[frame="void"] {
border-style: none;
}
div.tableblock > table[frame="hsides"] {
border-left-style: none;
border-right-style: none;
}
div.tableblock > table[frame="vsides"] {
border-top-style: none;
border-bottom-style: none;
}
/*
* html5 specific
*
* */
table.tableblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
thead, p.tableblock.header {
font-weight: bold;
color: #527bbd;
}
p.tableblock {
margin-top: 0;
}
table.tableblock {
border-width: 3px;
border-spacing: 0px;
border-style: solid;
border-color: #527bbd;
border-collapse: collapse;
}
th.tableblock, td.tableblock {
border-width: 1px;
padding: 4px;
border-style: solid;
border-color: #527bbd;
}
table.tableblock.frame-topbot {
border-left-style: hidden;
border-right-style: hidden;
}
table.tableblock.frame-sides {
border-top-style: hidden;
border-bottom-style: hidden;
}
table.tableblock.frame-none {
border-style: hidden;
}
th.tableblock.halign-left, td.tableblock.halign-left {
text-align: left;
}
th.tableblock.halign-center, td.tableblock.halign-center {
text-align: center;
}
th.tableblock.halign-right, td.tableblock.halign-right {
text-align: right;
}
th.tableblock.valign-top, td.tableblock.valign-top {
vertical-align: top;
}
th.tableblock.valign-middle, td.tableblock.valign-middle {
vertical-align: middle;
}
th.tableblock.valign-bottom, td.tableblock.valign-bottom {
vertical-align: bottom;
}
/*
* manpage specific
*
* */
body.manpage h1 {
padding-top: 0.5em;
padding-bottom: 0.5em;
border-top: 2px solid silver;
border-bottom: 2px solid silver;
}
body.manpage h2 {
border-style: none;
}
body.manpage div.sectionbody {
margin-left: 3em;
}
@media print {
body.manpage div#toc { display: none; }
}
@media screen {
body {
max-width: 50em; /* approximately 80 characters wide */
margin-left: 16em;
}
#toc {
position: fixed;
top: 0;
left: 0;
bottom: 0;
width: 13em;
padding: 0.5em;
padding-bottom: 1.5em;
margin: 0;
overflow: auto;
border-right: 3px solid #f8f8f8;
background-color: white;
}
#toc .toclevel1 {
margin-top: 0.5em;
}
#toc .toclevel2 {
margin-top: 0.25em;
display: list-item;
color: #aaaaaa;
}
#toctitle {
margin-top: 0.5em;
}
}
</style>
<script type="text/javascript">
/*<+'])');
// Function that scans the DOM tree for header elements (the DOM2
// nodeIterator API would be a better technique but not supported by all
// browsers).
var iterate = function (el) {
for (var i = el.firstChild; i != null; i = i.nextSibling) {
if (i.nodeType == 1 /* Node.ELEMENT_NODE */) {
var mo = re.exec(i.tagName);
if (mo && (i.getAttribute("class") || i.getAttribute("className")) != "float") {
result[result.length] = new TocEntry(i, getText(i), mo[1]-1);
}
iterate(i);
}
}
}
iterate(el);
return result;
}
var toc = document.getElementById("toc");
if (!toc) {
return;
}
// Delete existing TOC entries in case we're reloading the TOC.
var tocEntriesToRemove = [];
var i;
for (i = 0; i < toc.childNodes.length; i++) {
var entry = toc.childNodes[i];
if (entry.nodeName.toLowerCase() == 'div'
&& entry.getAttribute("class")
&& entry.getAttribute("class").match(/^toclevel/))
tocEntriesToRemove.push(entry);
}
for (i = 0; i < tocEntriesToRemove.length; i++) {
toc.removeChild(tocEntriesToRemove[i]);
}
// Rebuild TOC entries.
var entries = tocEntries(document.getElementById("content"), toclevels);
for (var i = 0; i < entries.length; ++i) {
var entry = entries[i];
if (entry.element.id == "")
entry.element.id = "_toc_" + i;
var a = document.createElement("a");
a.href = "#" + entry.element.id;
a.appendChild(document.createTextNode(entry.text));
var div = document.createElement("div");
div.appendChild(a);
div.className = "toclevel" + entry.toclevel;
toc.appendChild(div);
}
if (entries.length == 0)
toc.parentNode.removeChild(toc);
},
/////////////////////////////////////////////////////////////////////
// Footnotes generator
/////////////////////////////////////////////////////////////////////
/* Based on footnote generation code from:
* http://www.brandspankingnew.net/archive/2005/07/format_footnote.html
*/
footnotes: function () {
// Delete existing footnote entries in case we're reloading the footnodes.
var i;
var noteholder = document.getElementById("footnotes");
if (!noteholder) {
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<body class="book">
<div id="header">
<h1>The Erlang Runtime System</h1>
<div id="toc">
<div id="toctitle">Table of Contents</div>
<noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_preface">Preface</h2>
<div class="sectionbody">
<div class="paragraph"><p>This book is not about how to write correct and
beautiful code, I am assuming that you already know how to do
that. This book isn’t really about profiling and performance tuning
either. Although, there is a chapter in this book on tracing and
profiling which can help you find bottlenecks and unnecessary usage of
resources. There also is a chapter on performance tuning.</p></div>
<div class="paragraph"><p>These two chapters are the last chapters in the book, and the whole
book is building up to those chapters, but the real goal with this
book is to give you all the information, all the gory details, that
you need in order to really understand the performance of your Erlang
application.</p></div>
<div class="sect2">
<h3 id="who_is_this_book_for">About this book</h3>
<div class="paragraph"><p>For anyone who: Want to tune an Erlang installation. Want to know how
to debug VM crashes. Want to improve performance of Erlang
applications. Want to understand how Erlang really works. Want to
learn how to build your own runtime environment.</p></div>
<div class="paragraph"><p>If you want to debug the VM If you want to extend the VM If you want
to do performance tweaking—jump to the last chapter … but to really
understand that chapter you need to read the book.</p></div>
</div>
<div class="sect2">
<h3 id="_how_to_read_this_book">How to read this book</h3>
<div class="paragraph"><p>The Erlang RunTime System (ERTS) is a complex system with many
interdependent components. It is written in a very portable way so
that it can run on anything from a gum-stick computer to the largest
multicore system with terabytes of memory. In order to be able to
optimize the performance of such a system for your application, you
need to not only know your application, but you also need to have a
thorough understanding of ERTS itself.</p></div>
<div class="paragraph"><p>With this knowledge of how ERTS works you will be able to understand
how your application behaves when running on ERTS, and you will also
be able to find and fix problems with the performance of your application.
In the second part of this book we will go through how you successfully
run, monitor and scale your ERTS application.</p></div>
<div class="paragraph"><p>You don’t need to be an Erlang programmer to read this book, but you
will need some basic understanding of what Erlang is. This following
section will give you some Erlang background.</p></div>
</div>
<div class="sect2">
<h3 id="_erlang">Erlang</h3>
<div class="paragraph"><p>In this section we will look at some basic Erlang concepts that
are vital to understanding the rest of the book.</p></div>
<div class="paragraph"><p>Erlang has been called, especially by one of Erlang’s creators Joe
Armstrong, a concurrency oriented language. Concurrency is definitely
at the heart of Erlang, and to be able to understand how an Erlang
system works you need to understand the concurrency model of Erlang.</p></div>
<div class="paragraph"><p>First of all we need to make a distinction between <em>concurrency</em> and
<em>parallelism</em>. In this book <em>concurrency</em> is the concept of having
two or more processes that <strong>can</strong> execute independently of each other,
this can be done by first executing one process then the other or by
interleaving the execution, or by executing the processes in
parallel. With <em>parallel</em> executions we mean that the processes
actually execute at the exact same time by using several physical
execution units. Parallelism can be achieved on different levels.
Through multiple execution units in the execution pipeline in one core,
in several cores on one CPU, by several CPUs in one machine or through
several machines.</p></div>
<div class="paragraph"><p>Erlang uses processes to achieve concurrency. Conceptually Erlang
processes are similar to most OS processes, they execute in parallel
and can communicate through signals. In practices there is a huge
difference in that Erlang processes are much more lightweight than
most OS processes. Many other concurrent programming languages call
their equivalent to Erlang processes <em>agents</em>.</p></div>
<div class="paragraph"><p>Erlang achieves concurrency by interleaving the execution of processes
on the Erlang virtual machine, the BEAM. On multi-core processor the
BEAM can also achieve parallelism by running one scheduler per core and
executing one Erlang process per scheduler. The designer of an Erlang
system can achieve further parallelism by distributing the system on
several computers.</p></div>
<div class="paragraph"><p>A typical Erlang system (a server or service built in Erlang) consists
of a number of Erlang <em>applications</em>, corresponding to a directory on disk.
Each application is made up of several Erlang <em>modules</em> corresponding to
files in the directory. Each module contains a number of <em>functions</em> and
each function is made up of <em>expressions</em>.</p></div>
<div class="paragraph"><p>Since Erlang is a functional language it has no statements,
only expressions. Erlang expressions can be combined to an Erlang
function. A function takes a number of arguments and returns a
value. In <a href="#erlang_code_examples">[erlang_code_examples]</a> we can see some examples of
Erlang expressions and functions.</p></div>
<div class="listingblock">
<a id="erlang_code_examples"></a>
<div class="title">Erlang Code Examples</div>
<div class="content"><!-- Generator: GNU source-highlight 3.1.7
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-style: italic"><span style="color: #9A1900">%% Some Erlang expressions:</span></span>
<span style="color: #000080">true</span><span style="color: #990000">.</span>
<span style="color: #993399">1</span><span style="color: #990000">+</span><span style="color: #993399">1</span><span style="color: #990000">.</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> (<span style="color: #009900">X</span> <span style="color: #990000">></span> <span style="color: #009900">Y</span>) <span style="color: #990000">-></span> <span style="color: #009900">X</span>; <span style="color: #000080">true</span> <span style="color: #990000">-></span> <span style="color: #009900">Y</span> <span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span>
<span style="font-style: italic"><span style="color: #9A1900">%% An Erlang function:</span></span>
<span style="font-weight: bold"><span style="color: #000000">max</span></span>(<span style="color: #009900">X</span>, <span style="color: #009900">Y</span>) <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> (<span style="color: #009900">X</span> <span style="color: #990000">></span> <span style="color: #009900">Y</span>) <span style="color: #990000">-></span> <span style="color: #009900">X</span>;
<span style="color: #000080">true</span> <span style="color: #990000">-></span> <span style="color: #009900">Y</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Erlang has a number of <em>built in functions</em> (or <em>BIFs</em>) which are
implemented by the VM. This is either for efficiency reasons, like the
implementation of <span class="monospaced">lists:append</span> (which could be implemented in
Erlang). It could also be to provide some low level functionality
which would be hard or impossible to implement in Erlang itself, like
<span class="monospaced">list_to_atom</span>.</p></div>
<div class="paragraph"><p>Since Erlang/OTP R13B03 you can also provide your own functions
implemented in C by using the <em>Native Implemented Functions</em> (<em>NIF</em>)
interface.</p></div>
</div>
<div class="sect2">
<h3 id="_acknowledgments">Acknowledgments</h3>
<div class="paragraph"><p>A big thank you to everyone who has contributed in some way by checking in
something:</p></div>
<div class="literalblock">
<div class="content monospaced">
<pre>Roberto Aloi
Alexandre Rodrigues
Ken Causey
Michał Piotrowski
Anthony Molinaro
Benjamin Tan Wei Hao
Cameron Price
Jan Lehnardt
PlatinumThinker
Yago Riveiro
Yoshihiro TANAKA</pre>
</div></div>
</div>
</div>
</div>
<h1 id="P-ERTS">Understanding ERTS</h1>
<div class="sect1">
<h2 id="introduction">Introducing the Erlang Runtime System</h2>
<div class="sectionbody">
<div class="paragraph"><p>The Erlang RunTime System (ERTS) is a complex system with many interdependent
components. It is written in a very portable way so that it can run on
anything from a gum stick computer to the largest multicore system
with terabytes of memory. In order to be able to optimize the
performance of such a system for your application, you need to not
only know your application, but you also need to have a thorough
understanding of ERTS itself.</p></div>
<div class="sect2">
<h3 id="_erts_and_the_erlang_runtime_system">ERTS and the Erlang Runtime System</h3>
<div class="paragraph"><p>There is a difference between any Erlang Runtime System and a specific implementation of an Erlang Runtime
System. "Erlang/OTP" by Ericsson is the de facto standard
implementation of Erlang and the Erlang Runtime System. In this book I
will refer to this implementation as <em>ERTS</em> or spelled out <em>Erlang
RunTime System</em> with a capital T. (See <a href="#ERTS">[ERTS]</a> for a definition of
OTP).</p></div>
<div class="paragraph"><p>There is no official definition of what an Erlang Runtime System is,
or what an Erlang Virtual Machine is. You could sort of imagine what
such an ideal Platonic system would look like by taking ERTS and
removing all the implementation specific details. This is
unfortunately a circular definition, since you need to know the
general definition to be able to identify an implementation specific
detail. In the Erlang world we are usually too pragmatic to worry about
this.</p></div>
<div class="paragraph"><p>I will try to use the term <em>Erlang Runtime System</em> to refer to the
general idea of any Erlang Runtime System as opposed to the specific
implementation by Ericsson which I’ll call the Erlang RunTime System
or usually just ERTS.</p></div>
<div class="paragraph"><p><strong>Note</strong> This book is mostly a book about ERTS in particular and only to
a small extent about any general Erlang Runtime System. If you assume
that I talk about the Ericsson implementation unless I clearly state
that I am talking about a general principle you will probably be
right.</p></div>
</div>
<div class="sect2">
<h3 id="_how_to_read_this_book_2">How to read this book</h3>
<div class="paragraph"><p>In <a href="#P-Running">[P-Running]</a> of this book I will show you how to tune the
runtime system for your application and how to profile and debug
your application and the runtime system. In order to really know
how to tune the system you also need to know the system. In
<a href="#P-ERTS">[P-ERTS]</a> of this book you will get a deep understanding of
how the runtime system works.</p></div>
<div class="paragraph"><p>In the following chapters of <a href="#P-ERTS">[P-ERTS]</a> I will try to explain each
component of the system by itself, in a separate chapter for each of
the major component. You should be able to read any one of these
chapters without having a full understanding of how the other
components are implemented, but you will need a basic understanding of
what each component is. The rest of this introductory chapter should
give you enough basic understanding and vocabulary to be able to jump
between the rest of the chapters in part one in any order you like.</p></div>
<div class="paragraph"><p>However, if you have the time I strongly recommend reading the book in
order the first time. Words that are specific to Erlang and ERTS or
used in a specific way in this book are usually explained at their
first occurrence. Then, when you know the vocabulary, you can come
back and use Part I as a reference whenever you have a problem with a
particular component.</p></div>
</div>
<div class="sect2">
<h3 id="ERTS">ERTS</h3>
<div class="paragraph"><p>In this section I will give a basic overview of the main components of
ERTS and some vocabulary needed to understand the more
detailed descriptions of each component in the following chapters.</p></div>
<div class="sect3">
<h4 id="_the_erlang_node_erts">The Erlang Node (ERTS)</h4>
<div class="paragraph"><p>An Erlang node is a running instance of ERTS (or
possibly another implementation of Erlang (see
<a href="#Other_Erlang_Implementations">[Other_Erlang_Implementations]</a>)).
In OO terminology one could say that an Erlang node is an object
of the Erlang Runtime System class.</p></div>
<div class="paragraph"><p>All execution of Erlang code is done within a node. An erlang node
corresponds to an OS process and you can have several Erlang nodes
running on one machine.</p></div>
<div class="paragraph"><p>Your Erlang program (or application) will run in one or more Erlang
nodes, and the performance of your program will depend not only on
your application code but also on all the layers below your code
in the <em>Erlang solution stack</em>. In particular if you are running
your code on top of ERTS you will need to know the components of
the <em>ERTS Stack</em>.</p></div>
<div class="paragraph"><p>In <a href="#the_erts_stack">[the_erts_stack]</a> you can see the ERTS Stack illustrated with
two Erlang nodes running on one machine.</p></div>
<div class="paragraph"><p>At the bottom of the stack there is the hardware you are running
on. The easiest way to improve the performance of your app is probably
to run it on better hardware. If economical or physical constraints
won’t let you upgrade your hardware you can start exploring higher
levels of the stack. The two most important choices for your hardware
is whether it is multicore and whether it is 32-bit or 64-bit. You
need different builds of ERTS depending on whether you want to use
multicore or not and whether you want to use 32-bit or 64-bit. (See
<a href="#CH-BuildingERTS">[CH-BuildingERTS]</a> for information on how to build different