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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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Chapter 13. The DbTxn Handle</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="index.html" title="Berkeley DB C++ API Reference" />
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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">Chapter 13.
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The DbTxn Handle
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</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="seqstat_print.html">Prev</a> </td>
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<th width="60%" align="center"> </th>
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<td width="20%" align="right"> <a accesskey="n" href="dbget_transactional.html">Next</a></td>
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<div class="chapter" 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"><a id="txn"></a>Chapter 13.
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The DbTxn Handle
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</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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class DbTxn {
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public:
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DB_TXN *DbTxn::get_DB_TXN();
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const DB_TXN *DbTxn::get_const_DB_TXN() const;
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static DbTxn *DbTxn::get_DbTxn(DB_TXN *txn);
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static const DbTxn *DbTxn::get_const_DbTxn(const DB_TXN *txn);
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...
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}; </pre>
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<p>
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The <code class="classname">DbTxn</code> object is the handle for a transaction. Methods of
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the <code class="classname">DbTxn</code> handle are used to configure, abort and commit the
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transaction. <code class="classname">DbTxn</code> handles are provided to
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<a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> methods in order
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to transactionally protect those database operations.
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</p>
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<p>
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<code class="classname">DbTxn</code> handles are not free-threaded; transactions handles
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may be used by multiple threads, but only serially, that is, the application must
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serialize access to the <code class="classname">DbTxn</code> handle. Once the
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<a class="xref" href="txnabort.html" title="DbTxn::abort()">DbTxn::abort()</a> or
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<a class="xref" href="txncommit.html" title="DbTxn::commit()">DbTxn::commit()</a> methods are called, the handle
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may not be accessed again, regardless of the method's return. In addition, parent
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transactions may not issue any Berkeley DB operations while they have active child
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transactions (child transactions that have not yet been committed or aborted) except for
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<a class="xref" href="txnbegin.html" title="DbEnv::txn_begin()">DbEnv::txn_begin()</a>,
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<a class="xref" href="txnabort.html" title="DbTxn::abort()">DbTxn::abort()</a> and
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<a class="xref" href="txncommit.html" title="DbTxn::commit()">DbTxn::commit()</a>.
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</p>
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<p>
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Each <code class="classname">DbTxn</code> object has an associated
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<code class="literal">DB_TXN</code> struct, which is used by the underlying
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implementation of Berkeley DB and its
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<span>C++ language</span>
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API. The <code class="methodname">DbTxn::get_DB_TXN()</code> method
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returns a pointer to this struct. Given a const <code class="literal">DbTxn</code> object,
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<code class="methodname">txnMget_const_DB_TXN()</code>
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returns a const pointer to the same struct.
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</p>
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<p>
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Given a <code class="literal">DB_TXN</code> struct, the <code class="methodname">DbTxn::get_DbTxn()</code>
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method returns the corresponding <code class="classname">DbTxn</code> object, if there is
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one. If the <code class="literal">DB_TXN</code> object was not associated with a
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<code class="classname">DbTxn</code> (that is, it was not returned from a call to
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<code class="methodname">DbTxn::get_DB_TXN()</code>), then the result of
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<code class="methodname">DbTxn::get_DbTxn</code> is undefined. Given a const
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<code class="literal">DB_TXN</code> struct, <code class="methodname">DbTxn::get_const_DbTxn()</code>
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returns the associated const <code class="literal">DbTxn</code> object, if there is one.
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</p>
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<p>
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These methods may be useful for Berkeley DB applications including both C and C++
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language software. It should not be necessary to use these calls in a purely C++
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application.
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</p>
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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="txnlist"></a>Transaction Subsystem and Related Methods</h2>
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</div>
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</div>
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</div>
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<div class="navtable">
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<table border="1" width="80%">
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<thead>
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<tr>
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<th>Transaction Subsystem and Related Methods</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>
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<a class="xref" href="txnrecover.html" title="DbEnv::txn_recover()">DbEnv::txn_recover()</a>
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</td>
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<td>Distributed transaction recovery</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txncheckpoint.html" title="DbEnv::txn_checkpoint()">DbEnv::txn_checkpoint()</a>
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</td>
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<td>Checkpoint the transaction subsystem</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txnstat.html" title="DbEnv::txn_stat()">DbEnv::txn_stat()</a>
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</td>
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<td>Return transaction subsystem statistics</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txnstat_print.html" title="DbEnv::txn_stat_print()">DbEnv::txn_stat_print()</a>
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</td>
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<td>Print transaction subsystem statistics</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txnset_timeout.html" title="DbTxn::set_timeout()">DbTxn::set_timeout()</a>
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</td>
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<td>Set transaction timeout</td>
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</tr>
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<tr>
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<td colspan="2">
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<span class="bold">
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<strong>Transaction Subsystem Configuration</strong>
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</span>
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</td>
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</tr>
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<tr>
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<td><a class="xref" href="envset_timeout.html" title="DbEnv::set_timeout()">DbEnv::set_timeout()</a>, <a class="xref" href="envget_timeout.html" title="DbEnv::get_timeout()">DbEnv::get_timeout()</a></td>
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<td>Set/get lock and transaction timeout</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="dbget_transactional.html" title="Db::get_transactional()">Db::get_transactional()</a>
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</td>
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<td>Does the Db have transaction support</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="envcdsgroup_begin.html" title="DbEnv::cdsgroup_begin()">DbEnv::cdsgroup_begin()</a>
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</td>
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<td>Get a locker ID in Berkeley DB Concurrent Data Store</td>
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</tr>
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<tr>
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<td><a class="xref" href="envset_tx_max.html" title="DbEnv::set_tx_max()">DbEnv::set_tx_max()</a>, <a class="xref" href="envget_tx_max.html" title="DbEnv::get_tx_max()">DbEnv::get_tx_max()</a></td>
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<td>Set/get maximum number of transactions</td>
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</tr>
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<tr>
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<td><a class="xref" href="envset_tx_timestamp.html" title="DbEnv::set_tx_timestamp()">DbEnv::set_tx_timestamp()</a>, <a class="xref" href="envget_tx_timestamp.html" title="DbEnv::get_tx_timestamp()">DbEnv::get_tx_timestamp()</a></td>
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<td>Set/get recovery timestamp</td>
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</tr>
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<tr>
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<td colspan="2">
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<span class="bold">
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<strong>Transaction Operations</strong>
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</span>
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</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txnbegin.html" title="DbEnv::txn_begin()">DbEnv::txn_begin()</a>
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</td>
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<td>Begin a transaction</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txnabort.html" title="DbTxn::abort()">DbTxn::abort()</a>
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</td>
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<td>Abort a transaction</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txncommit.html" title="DbTxn::commit()">DbTxn::commit()</a>
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</td>
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<td>Commit a transaction</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txndiscard.html" title="DbTxn::discard()">DbTxn::discard()</a>
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</td>
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<td>Discard a prepared but not resolved transaction handle</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txnid.html" title="DbTxn::id()">DbTxn::id()</a>
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</td>
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<td>Return a transaction's ID</td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="txnprepare.html" title="DbTxn::prepare()">DbTxn::prepare()</a>
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</td>
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<td>Prepare a transaction for commit</td>
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</tr>
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<tr>
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<td><a class="xref" href="txnset_name.html" title="DbTxn::set_name()">DbTxn::set_name()</a>, <a class="xref" href="txnget_name.html" title="DbTxn::get_name()">DbTxn::get_name()</a></td>
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<td>Associate a string with a transaction</td>
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</tr>
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<tr>
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<td><a class="xref" href="txnset_priority.html" title="DbTxn::set_priority()">DbTxn::set_priority()</a>, <a class="xref" href="txnget_priority.html" title="DbTxn::get_priority()">DbTxn::get_priority()</a></td>
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<td>Set/get transaction's priority</td>
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</tr>
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</tbody>
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</table>
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</div>
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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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<tr>
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<td width="40%" align="left"><a accesskey="p" href="seqstat_print.html">Prev</a> </td>
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<td width="20%" align="center"> </td>
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<td width="40%" align="right"> <a accesskey="n" href="dbget_transactional.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">DbSequence::stat_print() </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::get_transactional()</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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