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diff --git a/system/doc/efficiency_guide/advanced.xml b/system/doc/efficiency_guide/advanced.xml new file mode 100644 index 0000000000..0ec3afbd59 --- /dev/null +++ b/system/doc/efficiency_guide/advanced.xml @@ -0,0 +1,204 @@ +<?xml version="1.0" encoding="latin1" ?> +<!DOCTYPE chapter SYSTEM "chapter.dtd"> + +<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 + compliance with the License. You should have received a copy of the + Erlang Public License along with this software. If not, it can be + retrieved online at http://www.erlang.org/. + + Software distributed under the License is distributed on an "AS IS" + basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See + the License for the specific language governing rights and limitations + under the License. + + </legalnotice> + + <title>Advanced</title> + <prepared>Kenneth Lundin</prepared> + <docno></docno> + <date>2001-08-21</date> + <rev></rev> + <file>advanced.xml</file> + </header> + + <section> + <title>Memory</title> + <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 + 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> + <row> + <cell align="center" valign="middle">Data type</cell> + <cell align="center" valign="middle">Memory size</cell> + </row> + <row> + <cell align="left" valign="middle">Integer (-16#7FFFFFF < i <16#7FFFFFF)</cell> + <cell align="left" valign="middle">1 word</cell> + </row> + <row> + <cell align="left" valign="middle">Integer (big numbers)</cell> + <cell align="left" valign="middle">3..N words</cell> + </row> + <row> + <cell align="left" valign="middle">Atom</cell> + <cell 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 <em>not</em> garbage-collected.</cell> + </row> + <row> + <cell align="left" valign="middle">Float</cell> + <cell align="left" valign="middle">On 32-bit architectures: 4 words <br></br> +On 64-bit architectures: 3 words</cell> + </row> + <row> + <cell align="left" valign="middle">Binary</cell> + <cell align="left" valign="middle">3..6 + data (can be shared)</cell> + </row> + <row> + <cell align="left" valign="middle">List</cell> + <cell align="left" valign="middle">1 word per element + the size of each element</cell> + </row> + <row> + <cell align="left" valign="middle">String (is the same as a list of integers)</cell> + <cell align="left" valign="middle">2 words per character</cell> + </row> + <row> + <cell align="left" valign="middle">Tuple</cell> + <cell align="left" valign="middle">2 words + the size of each element</cell> + </row> + <row> + <cell align="left" valign="middle">Pid</cell> + <cell 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.</cell> + </row> + <row> + <cell align="left" valign="middle">Port</cell> + <cell 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.</cell> + </row> + <row> + <cell align="left" valign="middle">Reference</cell> + <cell 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></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.</cell> + </row> + <row> + <cell align="left" valign="middle">Fun</cell> + <cell align="left" valign="middle">9..13 words + size of environment. Note: a fun refers into a fun table which also consumes memory.</cell> + </row> + <row> + <cell align="left" valign="middle">Ets table</cell> + <cell align="left" valign="middle">Initially 768 words + the size of each element (6 words + size of Erlang data). The table will grow when necessary.</cell> + </row> + <row> + <cell align="left" valign="middle">Erlang process</cell> + <cell align="left" valign="middle">327 words when spawned including a heap of 233 words.</cell> + </row> + <tcaption>Memory size of different data types</tcaption> + </table> + </section> + + <section> + <title>System limits</title> + <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> + <taglist> + <tag><em>Processes</em></tag> + <item> + <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 + <seealso marker="erts:erl#max_processes">+P</seealso> in the + <seealso marker="erts:erl">erl(1)</seealso> documentation). + The maximum limit of 268435456 processes will at least on a 32-bit + architecture be impossible to reach due to memory shortage.</p> + </item> + <tag><em>Distributed nodes</em></tag> + <item> + <taglist> + <tag>Known nodes</tag> + <item> + <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 + <seealso marker="#atoms">maximum number of atoms</seealso> + available for node names. All data concerning remote nodes, + except for the node name atom, are garbage-collected.</p> + </item> + <tag>Connected nodes</tag> + <item>The maximum number of simultaneously connected nodes is limited by + either the maximum number of simultaneously known remote nodes, + <seealso marker="#ports">the maximum number of (Erlang) ports</seealso> + available, or + <seealso marker="#files_sockets">the maximum number of sockets</seealso> + available.</item> + </taglist> + </item> + <tag><em>Characters in an atom</em></tag> + <item>255</item> + <tag><em>Atoms </em></tag> + <item> <marker id="atoms"></marker> +The maximum number of atoms is 1048576. </item> + <tag><em>Ets-tables</em></tag> + <item>The default is 1400, can be changed with the environment variable <c>ERL_MAX_ETS_TABLES</c>.</item> + <tag><em>Elements in a tuple</em></tag> + <item>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. </item> + <tag><em>Size of binary</em></tag> + <item>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 + <c>system_limit</c> 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 + <c>list_to_binary/1</c>) will probably also enforce the same limit.</item> + <tag><em>Total amount of data allocated by an Erlang node</em></tag> + <item>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.</item> + <tag><em>length of a node name</em></tag> + <item>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.</item> + <tag><em>Open ports</em></tag> + <item> + <marker id="ports"></marker> + <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 + <seealso marker="erts:erlang#ERL_MAX_PORTS">ERL_MAX_PORTS</seealso> + in <seealso marker="erts:erlang">erlang(3)</seealso>) + The maximum limit of 268435456 open ports will at least on a 32-bit + architecture be impossible to reach due to memory shortage.</p> + </item> + <tag><em>Open files, and sockets</em></tag> + <item> <marker id="files_sockets"></marker> + + The maximum number of simultaneously open files and sockets + depend on + <seealso marker="#ports">the maximum number of Erlang ports</seealso> + available, and operating system specific settings and limits.</item> + <tag><em>Number of arguments to a function or fun</em></tag> + <item>256</item> + </taglist> + </section> +</chapter> + |