<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html xmlns:fn="http://www.w3.org/2005/02/xpath-functions">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<link rel="stylesheet" href="../otp_doc.css" type="text/css">
<title>Erlang -- Advanced</title>
</head>
<body bgcolor="white" text="#000000" link="#0000ff" vlink="#ff00ff" alink="#ff0000"><div id="container">
<script id="js" type="text/javascript" language="JavaScript" src="../js/flipmenu/flipmenu.js"></script><script id="js2" type="text/javascript" src="../js/erlresolvelinks.js"></script><script language="JavaScript" type="text/javascript">
<!--
function getWinHeight() {
var myHeight = 0;
if( typeof( window.innerHeight ) == 'number' ) {
//Non-IE
myHeight = window.innerHeight;
} else if( document.documentElement && ( document.documentElement.clientWidth ||
document.documentElement.clientHeight ) ) {
//IE 6+ in 'standards compliant mode'
myHeight = document.documentElement.clientHeight;
} else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
//IE 4 compatible
myHeight = document.body.clientHeight;
}
return myHeight;
}
function setscrollpos() {
var objf=document.getElementById('loadscrollpos');
document.getElementById("leftnav").scrollTop = objf.offsetTop - getWinHeight()/2;
}
function addEvent(obj, evType, fn){
if (obj.addEventListener){
obj.addEventListener(evType, fn, true);
return true;
} else if (obj.attachEvent){
var r = obj.attachEvent("on"+evType, fn);
return r;
} else {
return false;
}
}
addEvent(window, 'load', setscrollpos);
//--></script><div id="leftnav"><div class="innertube">
<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>
<ul class="flipMenu" imagepath="../js/flipmenu">
<li id="no" title="Introduction" expanded="false">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="loadscrollpos" title="Advanced" expanded="true">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>10 Advanced</h1>
<h3><a name="id68919">10.1
Memory</a></h3>
<p>A good start when programming efficiently is to have knowledge about
how much memory different data types and operations require. It is
implementation-dependent how much memory the Erlang data types and
other items consume, but here are some figures for the
erts-5.2 system (OTP release R9B). (There have been no significant
changes in R13.)</p>
<p>The unit of measurement is memory words. There exists both a 32-bit
and a 64-bit implementation, and a word is therefore, 4 bytes or
8 bytes, respectively.</p>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td align="left" valign="middle">Data type</td>
<td align="left" valign="middle">Memory size</td>
</tr>
<tr>
<td align="left" valign="middle">Small integer</td>
<td align="left" valign="middle">1 word<br>
On 32-bit architectures: -134217729 < i < 134217728 (28 bits)<br>
On 64-bit architectures: -576460752303423489 < i < 576460752303423488 (60 bits)</td>
</tr>
<tr>
<td align="left" valign="middle">Big integer</td>
<td align="left" valign="middle">3..N words</td>
</tr>
<tr>
<td align="left" valign="middle">Atom</td>
<td align="left" valign="middle">1 word. Note: an atom refers into
an atom table which also consumes memory.
The atom text is stored once for each unique atom in this table.
The atom table is <strong>not</strong> garbage-collected.</td>
</tr>
<tr>
<td align="left" valign="middle">Float</td>
<td align="left" valign="middle">On 32-bit architectures: 4 words <br>
On 64-bit architectures: 3 words</td>
</tr>
<tr>
<td align="left" valign="middle">Binary</td>
<td align="left" valign="middle">3..6 + data (can be shared)</td>
</tr>
<tr>
<td align="left" valign="middle">List</td>
<td align="left" valign="middle">1 word + 1 word per element + the size of each element</td>
</tr>
<tr>
<td align="left" valign="middle">String (is the same as a list of integers)</td>
<td align="left" valign="middle">1 word + 2 words per character</td>
</tr>
<tr>
<td align="left" valign="middle">Tuple</td>
<td align="left" valign="middle">2 words + the size of each element</td>
</tr>
<tr>
<td align="left" valign="middle">Pid</td>
<td align="left" valign="middle">1 word for a process identifier from the current local node, and 5 words for a process identifier from another node. Note: a process identifier refers into a process table and a node table which also consumes memory.</td>
</tr>
<tr>
<td align="left" valign="middle">Port</td>
<td align="left" valign="middle">1 word for a port identifier from the current local node, and 5 words for a port identifier from another node. Note: a port identifier refers into a port table and a node table which also consumes memory.</td>
</tr>
<tr>
<td align="left" valign="middle">Reference</td>
<td align="left" valign="middle">On 32-bit architectures: 5 words for a reference from the current local node, and 7 words for a reference from another node. <br>
On 64-bit architectures: 4 words for a reference from the current local node, and 6 words for a reference from another node. Note: a reference refers into a node table which also consumes memory.</td>
</tr>
<tr>
<td align="left" valign="middle">Fun</td>
<td align="left" valign="middle">9..13 words + size of environment. Note: a fun refers into a fun table which also consumes memory.</td>
</tr>
<tr>
<td align="left" valign="middle">Ets table</td>
<td align="left" valign="middle">Initially 768 words + the size of each element (6 words + size of Erlang data). The table will grow when necessary.</td>
</tr>
<tr>
<td align="left" valign="middle">Erlang process</td>
<td align="left" valign="middle">327 words when spawned including a heap of 233 words.</td>
</tr>
</table>
<em>Table
10.1:
Memory size of different data types</em>
<h3><a name="id69276">10.2
System limits</a></h3>
<p>The Erlang language specification puts no limits on number of processes,
length of atoms etc., but for performance and memory saving reasons,
there will always be limits in a practical implementation of the Erlang
language and execution environment.</p>
<dl>
<dt><strong><strong>Processes</strong></strong></dt>
<dd>
<p>The maximum number of simultaneously alive Erlang processes is
by default 32768. This limit can be raised up to at most 268435456
processes at startup (see documentation of the system flag
<span class="bold_code"><a href="javascript:erlhref('../../','erts','erl.html#max_processes');">+P</a></span> in the
<span class="bold_code"><a href="javascript:erlhref('../../','erts','erl.html');">erl(1)</a></span> documentation).
The maximum limit of 268435456 processes will at least on a 32-bit
architecture be impossible to reach due to memory shortage.</p>
</dd>
<dt><strong><strong>Distributed nodes</strong></strong></dt>
<dd>
<dl>
<dt><strong>Known nodes</strong></dt>
<dd>
<p>A remote node Y has to be known to node X if there exist
any pids, ports, references, or funs (Erlang data types) from Y
on X, or if X and Y are connected. The maximum number of remote
nodes simultaneously/ever known to a node is limited by the
<span class="bold_code"><a href="#atoms">maximum number of atoms</a></span>
available for node names. All data concerning remote nodes,
except for the node name atom, are garbage-collected.</p>
</dd>
<dt><strong>Connected nodes</strong></dt>
<dd>The maximum number of simultaneously connected nodes is limited by
either the maximum number of simultaneously known remote nodes,
<span class="bold_code"><a href="#ports">the maximum number of (Erlang) ports</a></span>
available, or
<span class="bold_code"><a href="#files_sockets">the maximum number of sockets</a></span>
available.</dd>
</dl>
</dd>
<dt><strong><strong>Characters in an atom</strong></strong></dt>
<dd>255</dd>
<dt><strong><strong>Atoms </strong></strong></dt>
<dd> <a name="atoms"></a>
By default, the maximum number of atoms is 1048576.
This limit can be raised or lowered using the <span class="code">+t</span> option.</dd>
<dt><strong><strong>Ets-tables</strong></strong></dt>
<dd>The default is 1400, can be changed with the environment variable <span class="code">ERL_MAX_ETS_TABLES</span>.</dd>
<dt><strong><strong>Elements in a tuple</strong></strong></dt>
<dd>The maximum number of elements in a tuple is 67108863 (26 bit unsigned integer). Other factors
such as the available memory can of course make it hard to create a tuple of that size. </dd>
<dt><strong><strong>Size of binary</strong></strong></dt>
<dd>In the 32-bit implementation of Erlang, 536870911 bytes is the
largest binary that can be constructed or matched using the bit syntax.
(In the 64-bit implementation, the maximum size is 2305843009213693951 bytes.)
If the limit is exceeded, bit syntax construction will fail with a
<span class="code">system_limit</span> exception, while any attempt to match a binary that is
too large will fail.
This limit is enforced starting with the R11B-4 release; in earlier releases,
operations on too large binaries would in general either fail or give incorrect
results.
In future releases of Erlang/OTP, other operations that create binaries (such as
<span class="code">list_to_binary/1</span>) will probably also enforce the same limit.</dd>
<dt><strong><strong>Total amount of data allocated by an Erlang node</strong></strong></dt>
<dd>The Erlang runtime system can use the complete 32 (or 64) bit address space,
but the operating system often limits a single process to use less than that.</dd>
<dt><strong><strong>Length of a node name</strong></strong></dt>
<dd>An Erlang node name has the form host@shortname or host@longname. The node name is
used as an atom within the system so the maximum size of 255 holds for the node name too.</dd>
<dt><strong><strong>Open ports</strong></strong></dt>
<dd>
<a name="ports"></a>
<p>The maximum number of simultaneously open Erlang ports is
by default 1024. This limit can be raised up to at most 268435456
at startup (see environment variable
<span class="bold_code"><a href="javascript:erlhref('../../','erts','erlang.html#ERL_MAX_PORTS');">ERL_MAX_PORTS</a></span>
in <span class="bold_code"><a href="javascript:erlhref('../../','erts','erlang.html');">erlang(3)</a></span>)
The maximum limit of 268435456 open ports will at least on a 32-bit
architecture be impossible to reach due to memory shortage.</p>
</dd>
<dt><strong><strong>Open files, and sockets</strong></strong></dt>
<dd> <a name="files_sockets"></a>
The maximum number of simultaneously open files and sockets
depend on
<span class="bold_code"><a href="#ports">the maximum number of Erlang ports</a></span>
available, and operating system specific settings and limits.</dd>
<dt><strong><strong>Number of arguments to a function or fun</strong></strong></dt>
<dd>255</dd>
</dl>
</div>
<div class="footer">
<hr>
<p>Copyright © 2001-2012 Ericsson AB. All Rights Reserved.</p>
</div>
</div>
</div></body>
</html>
distrib
>
Fedora
>
17
>
i386
>
media
>
updates
>
by-pkgid
>
675c8c8167236dfcf8d66da674f931e8
>
files
>
39
