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BerkeleyDB-Core-C-GSG.pdf
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CoreCursorUsage.html
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CoreDBAdmin.html
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CoreDbUsage.html
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CoreEnvUsage.html
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Cursors.html
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DBEntry.html
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DBOpenFlags.html
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DbUsage.html
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DeleteEntryWCursor.html
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Positioning.html
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PutEntryWCursor.html
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ReplacingEntryWCursor.html
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accessmethods.html
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btree.html
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concepts.html
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coreindexusage.html
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cstructs.html
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databaseLimits.html
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databases.html
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dbErrorReporting.html
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dbconfig.html
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gettingStarted.css
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gettingit.html
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introduction.html
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joins.html
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keyCreator.html
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moreinfo.html
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preface.html
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Editing: databases.html
<?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>Chapter 2. Databases</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="Getting Started with Berkeley DB" /> <link rel="up" href="index.html" title="Getting Started with Berkeley DB" /> <link rel="prev" href="gettingit.html" title="Getting and Using DB" /> <link rel="next" href="coredbclose.html" title="Closing Databases" /> </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">Chapter 2. Databases</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="gettingit.html">Prev</a> </td> <th width="60%" align="center"> </th> <td width="20%" align="right"> <a accesskey="n" href="coredbclose.html">Next</a></td> </tr> </table> <hr /> </div> <div class="chapter" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title"><a id="databases"></a>Chapter 2. Databases</h2> </div> </div> </div> <div class="toc"> <p> <b>Table of Contents</b> </p> <dl> <dt> <span class="sect1"> <a href="databases.html#DBOpen">Opening Databases</a> </span> </dt> <dt> <span class="sect1"> <a href="coredbclose.html">Closing Databases</a> </span> </dt> <dt> <span class="sect1"> <a href="DBOpenFlags.html">Database Open Flags</a> </span> </dt> <dt> <span class="sect1"> <a href="CoreDBAdmin.html">Administrative Methods</a> </span> </dt> <dt> <span class="sect1"> <a href="dbErrorReporting.html">Error Reporting Functions</a> </span> </dt> <dt> <span class="sect1"> <a href="CoreEnvUsage.html">Managing Databases in Environments</a> </span> </dt> <dt> <span class="sect1"> <a href="CoreDbUsage.html">Database Example</a> </span> </dt> </dl> </div> <p>In Berkeley DB, a database is a collection of <span class="emphasis"><em>records</em></span>. Records, in turn, consist of key/data pairings. </p> <p> Conceptually, you can think of a <span>database</span> as containing a two-column table where column 1 contains a key and column 2 contains data. Both the key and the data are managed using <code class="classname">DBT</code> <span>structures</span> (see <a class="xref" href="DBEntry.html" title="Chapter 3. Database Records">Database Records</a> for details on this <span>structure</span>). So, fundamentally, using a DB <span>database</span> involves putting, getting, and deleting database records, which in turns involves efficiently managing information <span>contained in </span> <code class="classname">DBT</code> <span>structures.</span> The next several chapters of this book are dedicated to those activities. </p> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="DBOpen"></a>Opening Databases</h2> </div> </div> </div> <p> To open a database, you must first use the <code class="function">db_create()</code> function to initialize a <code class="classname">DB</code> handle. Once you have initialized the <code class="classname">DB</code> handle, you use its <code class="methodname">open()</code> method to open the database. </p> <p> Note that by default, DB does not create databases if they do not already exist. To override this behavior, specify the <a class="link" href="DBOpenFlags.html" title="Database Open Flags"><code class="literal">DB_CREATE</code></a> flag on the <code class="methodname">open()</code> method. </p> <p> The following code fragment illustrates a database open: </p> <a id="c_db1"></a> <pre class="programlisting">#include <db.h> ... DB *dbp; /* DB structure handle */ u_int32_t flags; /* database open flags */ int ret; /* function return value */ /* Initialize the structure. This * database is not opened in an environment, * so the environment pointer is NULL. */ ret = db_create(&dbp, NULL, 0); if (ret != 0) { /* Error handling goes here */ } /* Database open flags */ flags = DB_CREATE; /* If the database does not exist, * create it.*/ /* open the database */ ret = dbp->open(dbp, /* DB structure pointer */ NULL, /* Transaction pointer */ "my_db.db", /* On-disk file that holds the database. */ NULL, /* Optional logical database name */ DB_BTREE, /* Database access method */ flags, /* Open flags */ 0); /* File mode (using defaults) */ if (ret != 0) { /* Error handling goes here */ }</pre> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="gettingit.html">Prev</a> </td> <td width="20%" align="center"> </td> <td width="40%" align="right"> <a accesskey="n" href="coredbclose.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Getting and Using DB </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Closing Databases</td> </tr> </table> </div> </body> </html>
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