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HTML
309 lines
12 KiB
HTML
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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->close()</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="db.html" title="Chapter 2. The DB Handle" />
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<link rel="prev" href="dbassociate_foreign.html" title="DB->associate_foreign()" />
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<link rel="next" href="dbcompact.html" title="DB->compact()" />
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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->close()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbassociate_foreign.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The DB Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="dbcompact.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="dbclose"></a>DB->close()</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->close(DB *db, u_int32_t flags); </pre>
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<p>
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The <code class="methodname">DB->close()</code> method flushes cached database information to
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disk, closes any open cursors, frees allocated resources, and
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closes underlying files. When the close operation for a cursor fails,
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the method returns a non-zero error value for the first instance of such an error,
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and continues to close the rest of the cursors and database handles.
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</p>
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<p>
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Although closing a database handle will close any open cursors, it
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is recommended that applications explicitly close all their
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<a class="link" href="dbc.html" title="Chapter 3. The DBcursor Handle">DBcursor</a> handles
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before closing the database. The reason why is that when
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the cursor is explicitly closed, the memory allocated for it is
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reclaimed; however, this will <span class="emphasis"><em>not</em></span> happen if
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you close a database while cursors are still opened.
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</p>
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<p>
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The same rule, for the same reasons, hold true for
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<a class="link" href="txn.html" title="Chapter 12. The DB_TXN Handle">DB_TXN</a>
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handles. Simply make sure you close all your transaction handles
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before closing your database handle.
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</p>
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<p>
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Because key/data pairs are cached in memory, applications should
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make a point to always either close database handles or sync their
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data to disk (using the <a class="xref" href="dbsync.html" title="DB->sync()">DB->sync()</a>
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method) before exiting, to ensure that any data cached in main memory are
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reflected in the underlying file system.
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</p>
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<p>
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When called on a database that is the primary database for a secondary
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index, the primary database should be closed only after all secondary
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indices referencing it have been closed.
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</p>
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<p>
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When multiple threads are using the <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
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concurrently, only a single thread may call the <code class="methodname">DB->close()</code> method.
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</p>
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<p>
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The <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> handle may not be
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accessed again after <code class="methodname">DB->close()</code> is called, regardless of its return.
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</p>
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<p>
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If you do not close the <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> handle explicitly, it will be closed when
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the environment handle that owns the <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> handle is closed.
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</p>
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<p>
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The <code class="methodname">DB->close()</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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The error values that <code class="methodname">DB->close()</code> method returns include the error values of <code class="methodname">DBcursor->close()</code> and the following:
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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="id3853165"></a>DB_LOCK_DEADLOCK</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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A transactional database environment operation was selected to resolve
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a deadlock.
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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="id3853495"></a>DB_LOCK_NOTGRANTED</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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A Berkeley DB Concurrent Data Store database environment configured
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for lock timeouts was unable to grant a lock in the allowed time.
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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="id3853581"></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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If the cursor is already closed; or if an invalid flag value or parameter was specified.
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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="id3853539"></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="id3853500"></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 be set to the following value:
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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="dbclose_DB_NOSYNC"></a>
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<code class="literal">DB_NOSYNC</code>
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</p>
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<p>
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Do not flush cached information to disk. This flag is a
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dangerous option. It should be set only if the application is doing
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logging (with transactions) so that the database is recoverable after
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a system or application crash, or if the database is always generated
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from scratch after any system or application crash.
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</p>
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<p>
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<span class="bold"><strong>It is important to understand that flushing
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cached information to disk only minimizes the window of opportunity
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for corrupted data.</strong></span> Although unlikely, it is possible for
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database corruption to happen if a system or application crash occurs
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while writing data to the database. To ensure that database
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corruption never occurs, applications must either: use transactions
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and logging with automatic recovery; use logging and
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application-specific recovery; or edit a copy of the database, and
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once all applications using the database have successfully called
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<code class="methodname">DB->close()</code>, atomically replace the original database with the
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updated copy.
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</p>
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<p>
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Note that this flag only works when the database
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has been opened using an environment.
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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="id3852422"></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->close()</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="id3853810"></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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<p>
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The error messages returned for the first error encountered when <code class="methodname">DB->close()</code> method closes any open cursors include:
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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="id3853769"></a>DB_LOCK_DEADLOCK</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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A transactional database environment operation was selected to resolve
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a deadlock.
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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="id3852596"></a>DB_LOCK_NOTGRANTED</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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A Berkeley DB Concurrent Data Store database environment configured
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for lock timeouts was unable to grant a lock in the allowed time.
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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="id3853818"></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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If the cursor is already closed; or if 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="id3853812"></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="id3853873"></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="db.html#dblist" title="Database and Related Methods">Database 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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|||
|
|
<table width="100%" summary="Navigation footer">
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|||
|
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<tr>
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|||
|
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<td width="40%" align="left"><a accesskey="p" href="dbassociate_foreign.html">Prev</a> </td>
|
|||
|
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<td width="20%" align="center">
|
|||
|
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<a accesskey="u" href="db.html">Up</a>
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|||
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</td>
|
|||
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<td width="40%" align="right"> <a accesskey="n" href="dbcompact.html">Next</a></td>
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|||
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">DB->associate_foreign() </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"> DB->compact()</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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