mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
108 lines
4.6 KiB
HTML
108 lines
4.6 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Database limits</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="am_misc.html" title="Chapter 4. Access Method Wrapup" />
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<link rel="prev" href="am_misc_stability.html" title="Cursor stability" />
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<link rel="next" href="am_misc_diskspace.html" title="Disk space requirements" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 18.1.40</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Database limits</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="am_misc_stability.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4. Access Method Wrapup </th>
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<td width="20%" align="right"> <a accesskey="n" href="am_misc_diskspace.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="am_misc_dbsizes"></a>Database limits</h2>
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</div>
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</div>
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</div>
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<p>
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The largest database file that Berkeley DB can handle
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depends on the page size selected by the application. Berkeley
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DB stores database file page numbers as unsigned 32-bit
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numbers and database file page sizes as unsigned 16-bit
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numbers. Using the maximum database page size of 65536, this
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results in a maximum database file size of
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2<sup>48</sup> (256 terabytes). The
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minimum database page size is 512 bytes, which results in a
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minimum maximum database size of
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2<sup>41</sup> (2 terabytes).
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</p>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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In order to store petabytes of data you can use
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multiple database files.
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</p>
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</div>
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<p>
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The largest database file Berkeley DB can support is
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potentially further limited if the host system does not have
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filesystem support for files larger than
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2<sup>32</sup>, including the ability to
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seek to absolute offsets within those files.
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</p>
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<p>
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The largest key or data item that Berkeley DB can support
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is 2<sup>32</sup>, or more likely limited by
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available memory. Specifically, while key and data byte
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strings may be of essentially unlimited length, any one of
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them must fit into available memory so that it can be returned
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to the application. As some of the Berkeley DB interfaces
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return both key and data items to the application, those
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interfaces will require that any key/data pair fit
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simultaneously into memory. Further, as the access methods may
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need to compare key and data items with other key and data
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items, it may be a requirement that any two key or two data
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items fit into available memory. Finally, when writing
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applications supporting transactions, it may be necessary to
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have an additional copy of any data item in memory for logging
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purposes.
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</p>
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<p>
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The maximum Btree depth is 255.
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</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="am_misc_stability.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="am_misc.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="am_misc_diskspace.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Cursor stability </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Disk space
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requirements</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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