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<h2 class="title" style="clear: both"><a id="txnprepare"></a>DbTxn::prepare()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
DbTxn::prepare(u_int8_t gid[DB_XIDDATASIZE]);</pre>
<p>
The <code class="methodname">DbTxn::prepare()</code> method initiates the beginning of a two-phase
commit.
</p>
<p>
In a distributed transaction environment, Berkeley DB can be used as a
local transaction manager. In this case, the distributed transaction
manager must send <span class="emphasis"><em>prepare</em></span> messages to each local
manager. The local manager must then issue a <code class="methodname">DbTxn::prepare()</code> and
await its successful return before responding to the distributed
transaction manager. Only after the distributed transaction manager
receives successful responses from all of its
<span class="emphasis"><em>prepare</em></span> messages should it issue any
<span class="emphasis"><em>commit</em></span> messages.
</p>
<p>
In the case of nested transactions, preparing the parent causes all
unresolved children of the parent transaction to be committed. Child
transactions should never be explicitly prepared. Their fate will be
resolved along with their parent's during global recovery.
</p>
<p>
The <code class="methodname">DbTxn::prepare()</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>
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<h3 class="title"><a id="id1714462"></a>Parameters</h3>
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<h4 class="title"><a id="id1714940"></a>gid</h4>
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<p>
The <span class="bold"><strong>gid</strong></span> parameter specifies the
global transaction ID by which this transaction will be known. This
global transaction ID will be returned in calls
to <a class="xref" href="txnrecover.html" title="DbEnv::txn_recover()">DbEnv::txn_recover()</a>
telling the application which global transactions must be resolved.
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<h3 class="title"><a id="id1714463"></a>Class</h3>
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<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>
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<h3 class="title"><a id="id1714988"></a>See Also</h3>
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<a class="xref" href="txn.html#txnlist" title="Transaction Subsystem and Related Methods">Transaction Subsystem and Related Methods</a>
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