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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_GID_SIZE]);</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>
All open cursors in the transaction are closed and the
first cursor close error will be returned.
</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>
</span>
The errors that this method returns include the error values of <code class="methodname">Dbc::close()</code> and the following:
</p>
<div class="sect3" lang="en" xml:lang="en">
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<h4 class="title"><a id="idp5120248"></a><span>DbDeadlockException or </span>DB_LOCK_DEADLOCK</h4>
</div>
</div>
</div>
<p>
A transactional database environment operation was selected to resolve
a deadlock.
</p>
<p>
<a class="xref" href="dbdeadlock.html" title="DbDeadlockException">DbDeadlockException</a> is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, <code class="literal">DB_LOCK_DEADLOCK</code> is returned.
</p>
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<div class="sect3" lang="en" xml:lang="en">
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<h4 class="title"><a id="idp5128568"></a><span>DbLockNotGrantedException or </span>DB_LOCK_NOTGRANTED</h4>
</div>
</div>
</div>
<p>
A Berkeley DB Concurrent Data Store database environment configured
for lock timeouts was unable to grant a lock in the allowed time.
</p>
<p>
You attempted to open a database handle that is configured
for no waiting exclusive locking, but the exclusive lock could not be
immediately obtained. See
<a class="xref" href="dbset_lk_exclusive.html" title="Db::set_lk_exclusive()">Db::set_lk_exclusive()</a>
for more information.
</p>
<p>
<a class="xref" href="dblocknotgranted.html" title="DbLockNotGrantedException">DbLockNotGrantedException</a> is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, <code class="literal">DB_LOCK_NOTGRANTED</code> is returned.
</p>
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<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp5127496"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
If the cursor is already closed; or if an invalid flag value or parameter was specified.
</p>
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<div class="sect2" lang="en" xml:lang="en">
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<h3 class="title"><a id="idp5120488"></a>Parameters</h3>
</div>
</div>
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<div class="sect3" lang="en" xml:lang="en">
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<h4 class="title"><a id="idp5146696"></a>gid</h4>
</div>
</div>
</div>
<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.
</p>
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<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
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<h3 class="title"><a id="idp5138392"></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>
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<div class="sect2" lang="en" xml:lang="en">
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<h3 class="title"><a id="idp5138992"></a>See Also</h3>
</div>
</div>
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<p>
<a class="xref" href="txn.html#txnlist" title="Transaction Subsystem and Related Methods">Transaction Subsystem and Related Methods</a>
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