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303 lines
12 KiB
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<?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>DB->cursor()</title>
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<link rel="stylesheet" href="apiReference.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 C API Reference" />
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<link rel="up" href="dbc.html" title="Chapter 3. The DBcursor Handle" />
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<link rel="prev" href="dbc.html" title="Chapter 3. The DBcursor Handle" />
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<link rel="next" href="dbcclose.html" title="DBcursor->close()" />
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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">DB->cursor()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbc.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3.
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The DBcursor Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="dbcclose.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="dbcursor"></a>DB->cursor()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db.h>
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int
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DB->cursor(DB *db, DB_TXN *txnid, DBC **cursorp, u_int32_t flags); </pre>
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<p>
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The <code class="methodname">DB->cursor()</code> method returns a created database cursor.
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</p>
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<p>
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Cursors may span threads, but only serially, that is, the application
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must serialize access to the cursor handle.
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</p>
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<p>
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The <code class="methodname">DB->cursor()</code> <span>
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<span>
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method returns a non-zero error value on failure and 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" 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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<h3 class="title"><a id="id3876084"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3876073"></a>txnid</h4>
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</div>
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</div>
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</div>
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<p>
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To transaction-protect cursor operations, cursors must be
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opened and closed within the context of a transaction. The
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<span class="bold"><strong>txnid</strong></span> parameter specifies the
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transaction context in which the cursor may be used.
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</p>
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<p>
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Cursor operations are not automatically transaction-protected, even if the
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<a class="link" href="envset_flags.html#envset_flags_DB_AUTO_COMMIT">DB_AUTO_COMMIT</a>
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flag is specified to the
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<a class="xref" href="envset_flags.html" title="DB_ENV->set_flags()">DB_ENV->set_flags()</a> or
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<a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> methods. If
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cursor operations are to be transaction-protected, the <span class="bold"><strong>txnid</strong></span> parameter must be a transaction handle
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returned from <a class="xref" href="txnbegin.html" title="DB_ENV->txn_begin()">DB_ENV->txn_begin()</a>; otherwise,
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NULL.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3876303"></a>cursorp</h4>
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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 <span class="bold"><strong>cursorp</strong></span> parameter references
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memory into which a pointer to the allocated cursor is copied.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3876144"></a>flags</h4>
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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 <span class="bold"><strong>flags</strong></span> parameter must be set to 0
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or by bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing
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together one or more of the following values:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p><a id="cursor_DB_BULK"></a>
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<code class="literal">DB_CURSOR_BULK</code>
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</p>
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<p>
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Configure a cursor to optimize for bulk operations. Each
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successive operation on a cursor configured with this flag
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attempts to continue on the same database page as the previous
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operation, falling back to a search if a different page is
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required. This avoids searching if there is a high degree of
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locality between cursor operations. This flag is currently
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only effective with the btree access method. For other access
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methods, this flag is ignored.
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</p>
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</li>
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<li>
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<p><a id="cursor_DB_READ_COMMITTED"></a>
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<code class="literal">DB_READ_COMMITTED</code>
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</p>
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<p>
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Configure a transactional cursor to have degree 2 isolation. This
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ensures the stability of the current data item read by this cursor but
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permits data read by this cursor to be modified or deleted prior to
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the commit of the transaction for this cursor.
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</p>
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</li>
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<li>
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<p><a id="cursor_DB_READ_UNCOMMITTED"></a>
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<code class="literal">DB_READ_UNCOMMITTED</code>
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</p>
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<p>
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Configure a transactional cursor to have degree 1 isolation. Read
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operations performed by the cursor may return modified but not yet
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committed data. Silently ignored if the
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<a class="link" href="dbopen.html#dbopen_DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a>
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flag was not specified when the underlying database was opened.
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</p>
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</li>
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<li>
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<p><a id="cursor_DB_WRITECURSOR"></a>
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<code class="literal">DB_WRITECURSOR</code>
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</p>
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<p>
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Specify that the cursor will be used to update the database. The
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underlying database environment must have been opened using the
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<a class="link" href="envopen.html#envopen_DB_INIT_CDB">DB_INIT_CDB</a> flag.
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</p>
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</li>
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<li>
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<p><a id="cursor_DB_TXN_SNAPSHOT"></a>
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<code class="literal">DB_TXN_SNAPSHOT</code>
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</p>
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<p>
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Configure a transactional cursor to operate with read-only <a href="../../programmer_reference/transapp_read.html" class="olink">snapshot isolation</a>. For
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databases with the
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<a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a>
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flag set, data values will be read as they are when the cursor is
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opened, without taking read locks.
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</p>
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<p>
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This flag implicitly begins a transaction that is committed when the cursor is
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closed.
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</p>
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<p>
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This flag is silently ignored if
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<a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a>
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is not set on the underlying database or if a transaction is supplied in
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the <span class="bold"><strong>txnid</strong></span> parameter.
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</p>
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</li>
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</ul>
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</div>
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</div>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="id3876420"></a>Errors</h3>
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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 <code class="methodname">DB->cursor()</code> <span>
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<span>
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method may fail and return one of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" 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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<h4 class="title"><a id="id3876121"></a> DB_REP_HANDLE_DEAD</h4>
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</div>
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</div>
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</div>
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<p>
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When a client synchronizes with the master, it is possible for committed
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transactions to be rolled back. This invalidates all the database and cursor
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handles opened in the replication environment. Once this occurs, an attempt to use
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such a handle will
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return <code class="literal">DB_REP_HANDLE_DEAD</code>.
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The application will need to discard the handle and open a new one in order to
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continue processing.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3876247"></a>DB_REP_LOCKOUT</h4>
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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 operation was blocked by client/master synchronization.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3876407"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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An invalid flag value or parameter was specified.
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</p>
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</div>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="id3876072"></a>Class</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
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</p>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="id3876427"></a>See Also</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="xref" href="dbc.html#dbclist" title="Database Cursors and Related Methods">Database Cursors and Related Methods</a>
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</p>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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|||
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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="dbc.html">Prev</a> </td>
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|||
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<td width="20%" align="center">
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|||
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<a accesskey="u" href="dbc.html">Up</a>
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|||
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</td>
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|||
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<td width="40%" align="right"> <a accesskey="n" href="dbcclose.html">Next</a></td>
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|||
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</tr>
|
|||
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<tr>
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|||
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<td width="40%" align="left" valign="top">Chapter 3.
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|||
|
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The DBcursor Handle
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</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"> DBcursor->close()</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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