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The DbTxn Handle
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<div class="sect1" lang="en" xml:lang="en">
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<h2 class="title" style="clear: both"><a id="txnrecover"></a>DbEnv::txn_recover()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::txn_recover(DB_PREPLIST preplist[],
long count, long *retp, u_int32_t flags);</pre>
<p>
Database environment recovery restores transactions that were
prepared, but not yet resolved at the time of the system shut down or
crash, to their state prior to the shut down or crash, including any
locks previously held. The <code class="methodname">DbEnv::txn_recover()</code> method returns a
list of those prepared transactions.
</p>
<p>
The <code class="methodname">DbEnv::txn_recover()</code> method should only be called after the
environment has been recovered.
</p>
<p>
Multiple threads of control may call <code class="methodname">DbEnv::txn_recover()</code>, but only
one thread of control may resolve each returned transaction, that is,
only one thread of control may call <a class="xref" href="txncommit.html" title="DbTxn::commit()">DbTxn::commit()</a>
or <a class="xref" href="txnabort.html" title="DbTxn::abort()">DbTxn::abort()</a> on each
returned transaction. Callers of <code class="methodname">DbEnv::txn_recover()</code> must call
<a class="xref" href="txndiscard.html" title="DbTxn::discard()">DbTxn::discard()</a> to
discard each transaction they do not resolve.
</p>
<p>
On return from <code class="methodname">DbEnv::txn_recover()</code>, the <span class="bold"><strong>preplist</strong></span> parameter will be filled in with a list of transactions
that must be resolved by the application (committed, aborted or discarded). The <span class="bold"><strong>preplist</strong></span> parameter is a structure of type
<code class="literal">DB_PREPLIST</code>; the following <code class="literal">DB_PREPLIST</code> fields will be
filled in:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="bold"><strong>DB_TXN * txn;</strong></span>
</p>
<p>
The transaction handle for the transaction.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int8_t gid[DB_XIDDATASIZE];</strong></span>
</p>
<p>
The global transaction ID for the transaction. The global transaction
ID is the one specified when the transaction was prepared. The
application is responsible for ensuring uniqueness among global
transaction IDs.
</p>
</li>
</ul>
</div>
<p>
The <code class="methodname">DbEnv::txn_recover()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1715136"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1715480"></a>count</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>count</strong></span> parameter specifies the
number of available entries in the passed-in <span class="bold"><strong>preplist</strong></span> array. The <span class="bold"><strong>retp</strong></span> parameter returns the number of entries
<code class="methodname">DbEnv::txn_recover()</code> has filled in, in the array.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1715609"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to
one of the following values:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">DB_FIRST</code>
</p>
<p>
Begin returning a list of prepared, but not yet resolved transactions.
Specifying this flag begins a new pass over all prepared, but not yet
completed transactions, regardless of whether they have already been
returned in previous calls to <code class="methodname">DbEnv::txn_recover.()</code> Calls to
<code class="methodname">DbEnv::txn_recover()</code> from different threads of control should not be
intermixed in the same environment.
</p>
</li>
<li>
<p>
<code class="literal">DB_NEXT</code>
</p>
<p>
Continue returning a list of prepared, but not yet resolved
transactions, starting where the last call to
<code class="methodname">DbEnv::txn_recover()</code>
left off.
</p>
</li>
</ul>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1715105"></a>preplist</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>preplist</strong></span> parameter references
memory into which the list of transactions to be resolved by the
application is copied.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1715629"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>, <a class="link" href="txn.html" title="Chapter 13. The DbTxn Handle">DbTxn</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1715796"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="txn.html#txnlist" title="Transaction Subsystem and Related Methods">Transaction Subsystem and Related Methods</a>
</p>
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