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<h2 class="title" style="clear: both"><a id="xa_xa_restrict"></a>Restrictions on XA Transactions</h2>
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<p>
When you are using Berkeley DB for XA transactions, there
are a few restrictions you should be aware of:
</p>
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<li>
<p>
Configure environment using the <a href="../api_reference/C/configuration_reference.html" class="olink">DB_CONFIG</a> file
</p>
<p>
For most options, you must configure your
environment via the <a href="../api_reference/C/configuration_reference.html" class="olink">DB_CONFIG</a> file because an XA
application or server cannot control the environment
creation.
</p>
</li>
<li>
<p>
Snapshot isolation must be configured for the
entire environment.
</p>
<p>
Transactions managed by the Berkeley DB X/open
compliant XA resource manager can be configured for
transaction snapshots using either database open flags
or the <a href="../api_reference/C/configuration_reference.html" class="olink">DB_CONFIG</a> file file. To configure using database
open flags, open the XA managed database with the flag
<a href="../api_reference/C/dbopen.html#dbopen_DB_MULTIVERSION" class="olink">DB_MULTIVERSION</a>. When using DB_CONFIG, include both
of the following lines:
</p>
<pre class="programlisting">set_flags DB_MULTIVERSION
set_flags DB_TXN_SNAPSHOT</pre>
<p>
Note that both methods will results in all
transactions using transaction snapshots, there is no
way to enable transaction snapshots in just a subset
of XA managed transactions.
</p>
</li>
<li>
<p>
No in-memory logging
</p>
<p>
Upon return from xa_open, Berkeley DB checks to
ensure there is no in-memory logging. If in-memory
logging is detected, a FAILURE message is returned to
the application.
</p>
</li>
<li>
<p>
No application-level child transactions
</p>
<p>
Berkeley DB verifies in the xa_start and xa_end
calls that no XA transaction has a parent. If
application-level child transactions are detected, a
FAILURE message is returned to the application.
</p>
</li>
<li>
<p>
All database-level operations, such as create,
rename, and remove, must be performed in local BDB
transactions, not distributed XA transactions
</p>
<p>
Berkeley DB checks that there is no XA transaction
currently active during these operations, and if
detected, a FAILURE message is returned to the
application.
</p>
</li>
<li>
<p>
Close cursors before a service invocation returns
</p>
<p>
Berkeley DB checks in the <code class="literal">xa_end</code>
call that the <code class="literal">DB_TXN</code> has no active
cursors open and and if detected, a FAILURE message is
returned to the application.
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