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| author | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-07-20 20:00:05 +0100 |
|---|---|---|
| committer | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-07-20 20:00:05 +0100 |
| commit | 3ef782d3745ea8f25a3151561a3cfb882190210e (patch) | |
| tree | 86b9c2f5fde051dd0bced99b3fc9f5a3ba08db69 /docs/programmer_reference/mp_config.html | |
| download | berkeleydb-3ef782d3745ea8f25a3151561a3cfb882190210e.tar.gz | |
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| -rw-r--r-- | docs/programmer_reference/mp_config.html | 110 |
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diff --git a/docs/programmer_reference/mp_config.html b/docs/programmer_reference/mp_config.html new file mode 100644 index 00000000..ae7083aa --- /dev/null +++ b/docs/programmer_reference/mp_config.html @@ -0,0 +1,110 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <title>Configuring the memory pool</title> + <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> + <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> + <link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" /> + <link rel="up" href="mp.html" title="Chapter 18. The Memory Pool Subsystem" /> + <link rel="prev" href="mp.html" title="Chapter 18. The Memory Pool Subsystem" /> + <link rel="next" href="mp_warm.html" title="Warming the memory pool" /> + </head> + <body> + <div xmlns="" class="navheader"> + <div class="libver"> + <p>Library Version 11.2.5.3</p> + </div> + <table width="100%" summary="Navigation header"> + <tr> + <th colspan="3" align="center">Configuring the memory pool</th> + </tr> + <tr> + <td width="20%" align="left"><a accesskey="p" href="mp.html">Prev</a> </td> + <th width="60%" align="center">Chapter 18. + The Memory Pool Subsystem + </th> + <td width="20%" align="right"> <a accesskey="n" href="mp_warm.html">Next</a></td> + </tr> + </table> + <hr /> + </div> + <div class="sect1" lang="en" xml:lang="en"> + <div class="titlepage"> + <div> + <div> + <h2 class="title" style="clear: both"><a id="mp_config"></a>Configuring the memory pool</h2> + </div> + </div> + </div> + <p>There are two issues to consider when configuring the memory pool.</p> + <p>The first issue, the most important tuning parameter for Berkeley DB +applications, is the size of the memory pool. There are two ways to +specify the pool size. First, calling the <a href="../api_reference/C/envset_cachesize.html" class="olink">DB_ENV->set_cachesize()</a> method +specifies the pool size for all of the applications sharing the Berkeley DB +environment. Second, the <a href="../api_reference/C/dbset_cachesize.html" class="olink">DB->set_cachesize()</a> method only specifies a +pool size for the specific database. Note: It is meaningless to call +<a href="../api_reference/C/dbset_cachesize.html" class="olink">DB->set_cachesize()</a> for a database opened inside of a Berkeley DB +environment because the environment pool size will override any pool +size specified for a single database. For information on tuning the +Berkeley DB cache size, see +<a class="xref" href="general_am_conf.html#am_conf_cachesize" title="Selecting a cache size">Selecting a cache size</a>.</p> + <p> + Note the memory pool defaults to assuming that the average page size is + 4k. This factor is used to determine the size of the hash table used + to locate pages in the memory pool. The size of the hash table is + calculated to so that on average 2.5 pages will be in each hash table + entry. Each page requires a mutex be allocated to it and the average + page size is used to determine the number of mutexes to allocate to the + memory pool. +</p> + <p> + Normally you should see good results by using the default values for + the page size, but in some cases you may be able to achieve better + performance by manually configuring the page size. The expected page + size, hash table size and mutex count can be set via the methods: + <a href="../api_reference/C/envset_mp_pagesize.html" class="olink">DB_ENV->set_mp_pagesize()</a>, <a href="../api_reference/C/envset_mp_tablesize.html" class="olink">DB_ENV->set_mp_tablesize()</a>, and <a href="../api_reference/C/envset_mp_mtxcount.html" class="olink">DB_ENV->set_mp_mtxcount()</a>. +</p> + <p>The second memory pool configuration issue is the maximum size an +underlying file can be and still be mapped into the process address +space (instead of reading the file's pages into the cache). Mapping +files into the process address space can result in better performance +because available virtual memory is often much larger than the local +cache, and page faults are faster than page copying on many systems. +However, in the presence of limited virtual memory, it can cause +resource starvation; and in the presence of large databases, it can +result in immense process sizes. In addition, because of the +requirements of the Berkeley DB transactional implementation, only read-only +files can be mapped into process memory.</p> + <p>To specify that no files are to be mapped into the process address +space, specify the <a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a> flag to the +<a href="../api_reference/C/envset_flags.html" class="olink">DB_ENV->set_flags()</a> method. To specify that any individual file should +not be mapped into the process address space, specify the +<a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a> flag to the <a href="../api_reference/C/mempfopen.html" class="olink">DB_MPOOLFILE->open()</a> interface. To limit +the size of files mapped into the process address space, use the +<a href="../api_reference/C/envset_mp_mmapsize.html" class="olink">DB_ENV->set_mp_mmapsize()</a> method.</p> + </div> + <div class="navfooter"> + <hr /> + <table width="100%" summary="Navigation footer"> + <tr> + <td width="40%" align="left"><a accesskey="p" href="mp.html">Prev</a> </td> + <td width="20%" align="center"> + <a accesskey="u" href="mp.html">Up</a> + </td> + <td width="40%" align="right"> <a accesskey="n" href="mp_warm.html">Next</a></td> + </tr> + <tr> + <td width="40%" align="left" valign="top">Chapter 18. + The Memory Pool Subsystem + </td> + <td width="20%" align="center"> + <a accesskey="h" href="index.html">Home</a> + </td> + <td width="40%" align="right" valign="top"> Warming the memory pool</td> + </tr> + </table> + </div> + </body> +</html> |