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HTML
114 lines
6.7 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>Converting Applications</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 Upgrade Guide" />
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<link rel="up" href="upgrade_2_0_toc.html" title="Chapter 15. Upgrading Berkeley DB 1.85 or 1.86 applications to Berkeley DB 2.0" />
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<link rel="prev" href="upgrade_2_0_system.html" title="System Integration" />
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<link rel="next" href="upgrade_2_0_disk.html" title="Upgrade 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 11.2.5.2</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">Converting Applications</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="upgrade_2_0_system.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 15. Upgrading Berkeley DB 1.85 or 1.86 applications to Berkeley DB 2.0</th>
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<td width="20%" align="right"> <a accesskey="n" href="upgrade_2_0_disk.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="upgrade_2_0_convert"></a>Converting Applications</h2>
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</div>
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</div>
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</div>
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<p>Mapping the Berkeley DB 1.85 functionality into Berkeley DB version 2 is almost always
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simple. The manual page <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a> replaces the Berkeley DB 1.85 manual
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pages <code class="literal">dbopen</code>(3), <code class="literal">btree</code>(3), <code class="literal">hash</code>(3) and
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<code class="literal">recno</code>(3). You should be able to convert each 1.85 function
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call into a Berkeley DB version 2 function call using just the <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a>
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documentation.</p>
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<p>Some guidelines and things to watch out for:</p>
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<div class="orderedlist">
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<ol type="1">
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<li>Most access method functions have exactly the same semantics as in Berkeley DB
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1.85, although the arguments to the functions have changed in some cases.
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To get your code to compile, the most common change is to add the
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transaction ID as an argument (NULL, since Berkeley DB 1.85 did not support
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transactions.)</li>
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<li>You must always initialize DBT structures to zero before using them with
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any Berkeley DB version 2 function. (They do not normally have to be
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reinitialized each time, only when they are first allocated. Do this by
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declaring the DBT structure external or static, or by calling the C
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library routine <code class="literal">bzero</code>(3) or <code class="literal">memset</code>(3).)</li>
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<li>The error returns are completely different in the two versions. In Berkeley DB
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1.85, < 0 meant an error, and > 0 meant a minor Berkeley DB exception.
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In Berkeley DB 2.0, > 0 means an error (the Berkeley DB version 2 functions
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return <code class="literal">errno</code> on error) and < 0 means a Berkeley DB exception.
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See <a href="../programmer_reference/program_errorret.html" class="olink">Program returns to applications</a> for more information.</li>
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<li>The Berkeley DB 1.85 DB->seq function has been replaced by cursors in Berkeley DB
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version 2. The semantics are approximately the same, but cursors require
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the creation of an extra object (the DBC object), which is then used to
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access the database.
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<p>Specifically, the partial key match and range search functionality of the
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R_CURSOR flag in DB->seq has been replaced by the <a href="../api_reference/C/dbcget.html#dbcget_DB_SET_RANGE" class="olink">DB_SET_RANGE</a> flag in
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<a href="../api_reference/C/dbcget.html" class="olink">DBC->get()</a>.</p></li>
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<li>In version 2 of the Berkeley DB library, additions or deletions into Recno
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(fixed and variable-length record) databases no longer automatically
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logically renumber all records after the add/delete point, by default.
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The default behavior is that deleting records does not cause subsequent
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records to be renumbered, and it is an error to attempt to add new records
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between records already in the database. Applications wanting the
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historic Recno access method semantics should call the
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<a href="../api_reference/C/dbset_flags.html" class="olink">DB->set_flags()</a> method with the <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> flag.</li>
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<li>Opening a database in Berkeley DB version 2 is a much heavier-weight operation
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than it was in Berkeley DB 1.85. Therefore, if your historic applications were
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written to open a database, perform a single operation, and close the
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database, you may observe performance degradation. In most cases, this
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is due to the expense of creating the environment upon each open. While
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we encourage restructuring your application to avoid repeated opens and
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closes, you can probably recover most of the lost performance by simply
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using a persistent environment across invocations.</li>
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</ol>
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</div>
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<p>While simply converting Berkeley DB 1.85 function calls to Berkeley DB version 2
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function calls will work, we recommend that you eventually reconsider your
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application's interface to the Berkeley DB database library in light of the
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additional functionality supplied by Berkeley DB version 2, as it is likely to
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result in enhanced application performance.</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="upgrade_2_0_system.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="upgrade_2_0_toc.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="upgrade_2_0_disk.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">System Integration </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"> Upgrade 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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