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329 lines
14 KiB
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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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Db::key_range()</title>
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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="dbjoin.html" title="Db::join()" />
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<link rel="next" href="dbopen.html" title="Db::open()" />
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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::key_range()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbjoin.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="dbopen.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="dbkey_range"></a>Db::key_range()</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_cxx.h>
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int
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Db::key_range(DbTxn *txnid
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Dbt *key, DB_KEY_RANGE *key_range, u_int32_t flags);</pre>
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<p>
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The <code class="methodname">Db::key_range()</code> method returns an estimate of the proportion of
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keys that are less than, equal to, and greater than the specified key.
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The underlying database must be of type Btree.
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</p>
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<p>
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The <code class="methodname">Db::key_range()</code> method fills in a structure of type DB_KEY_RANGE.
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The following data fields are available from the DB_KEY_RANGE
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structure:
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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>
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<span class="bold"><strong>double less;</strong></span>
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</p>
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<p>
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A value between 0 and 1, the proportion of keys less than the
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specified key.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>double equal;</strong></span>
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</p>
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<p>
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A value between 0 and 1, the proportion of keys equal to the specified
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key.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>double greater;</strong></span>
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</p>
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<p>
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A value between 0 and 1, the proportion of keys greater than the
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specified key.
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</p>
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</li>
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</ul>
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</div>
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<p>
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Values are in the range of 0 to 1; for example, if the field <span class="bold"><strong>less</strong></span> is 0.05, 5% of the keys in the database
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are less than the <span class="bold"><strong>key</strong></span> parameter. The
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value for <span class="bold"><strong>equal</strong></span> will be zero if there
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is no matching key, and will be non-zero otherwise.
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</p>
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<p>
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The <code class="methodname">Db::key_range()</code> <span>
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<span>
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method either returns a non-zero error value or throws an
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exception that encapsulates a non-zero error value on
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failure, and returns 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="id3586861"></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="id3587190"></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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If the operation is part of an application-specified transaction, the
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<span class="bold"><strong>txnid</strong></span> parameter is a transaction
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handle returned from <a class="xref" href="txnbegin.html" title="DbEnv::txn_begin()">DbEnv::txn_begin()</a>;
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if the operation is part of a Berkeley DB Concurrent Data Store group, the
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<span class="bold"><strong>txnid</strong></span> parameter is a handle returned
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from <a class="xref" href="envcdsgroup_begin.html" title="DbEnv::cdsgroup_begin()">DbEnv::cdsgroup_begin()</a>;
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otherwise NULL. If no transaction handle is specified, but the
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operation occurs in a transactional database, the operation will be
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implicitly transaction protected. The <code class="methodname">Db::key_range()</code> method does not
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retain the locks it acquires for the life of the transaction, so
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estimates may not be repeatable.
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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="id3587398"></a>key</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 key <a class="link" href="dbt.html" title="Chapter 4. The Dbt Handle">Dbt</a> operated on.
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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="id3587648"></a>key_range</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 estimates are returned in the <span class="bold"><strong>key_range</strong></span> parameter, which contains three
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elements of type double: <span class="bold"><strong>less</strong></span>,
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<span class="bold"><strong>equal</strong></span>, and <span class="bold"><strong>greater</strong></span>. Values are in the range of 0 to 1;
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for example, if the field <span class="bold"><strong>less</strong></span> is
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0.05, 5% of the keys in the database are less than the <span class="bold"><strong>key</strong></span> parameter. The value for <span class="bold"><strong>equal</strong></span> will be zero if there is no matching key,
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and will be non-zero otherwise.
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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="id3587659"></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 is currently
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unused, and must be set to 0.
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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="id3587691"></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::key_range()</code> <span>
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<span>
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method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
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exception, encapsulating one of the following non-zero errors, or return one
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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="id3587815"></a><span>DbDeadlockException or </span>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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<p>
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<a class="xref" href="dbdeadlock.html" title="DbDeadlockException">DbDeadlockException</a> is thrown if
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your Berkeley DB API is configured to throw exceptions.
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Otherwise, <code class="literal">DB_LOCK_DEADLOCK</code> is returned.
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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="id3587872"></a><span>DbLockNotGrantedException or </span>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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<p>
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<a class="xref" href="dblocknotgranted.html" title="DbLockNotGrantedException">DbLockNotGrantedException</a> is thrown if
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your Berkeley DB API is configured to throw exceptions.
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Otherwise, <code class="literal">DB_LOCK_NOTGRANTED</code> is returned.
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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="id3587598"></a> <span>DbRepHandleDeadException or</span> 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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<span>
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throw a <a class="xref" href="dbrephandledead.html" title="DbRepHandleDeadException">DbRepHandleDeadException</a> (if
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your application is configured to throw exceptions), or
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</span>
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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="id3587919"></a><span>DbDeadlockException or </span>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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<p>
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<a class="xref" href="dbdeadlock.html" title="DbDeadlockException">DbDeadlockException</a> is thrown if
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your Berkeley DB API is configured to throw exceptions.
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Otherwise, <code class="literal">DB_REP_LOCKOUT</code> is returned.
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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="id3587937"></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 underlying database was not of type Btree; or if an invalid
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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="id3587718"></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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|||
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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="id3587955"></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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|||
|
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</div>
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|||
|
|
<div class="navfooter">
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|||
|
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<hr />
|
|||
|
|
<table width="100%" summary="Navigation footer">
|
|||
|
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<tr>
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|||
|
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<td width="40%" align="left"><a accesskey="p" href="dbjoin.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="db.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="dbopen.html">Next</a></td>
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|||
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</tr>
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|||
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<tr>
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|||
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<td width="40%" align="left" valign="top">Db::join() </td>
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|||
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<td width="20%" align="center">
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|||
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<a accesskey="h" href="index.html">Home</a>
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|||
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</td>
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|||
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<td width="40%" align="right" valign="top"> Db::open()</td>
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|||
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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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