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<div class="sect1" lang="en" xml:lang="en">
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<h2 class="title" style="clear: both"><a id="envset_app_dispatch"></a>DB_ENV->set_app_dispatch()</h2>
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<pre class="programlisting">#include <db.h>
int
DB_ENV->set_app_dispatch(DB_ENV *dbenv,
int (*tx_recover)(DB_ENV *dbenv,
DBT *log_rec, DB_LSN *lsn, db_recops op)); </pre>
<p>
Declare a function to be called during transaction abort and recovery
to process application-specific log records.
</p>
<p>
The <code class="methodname">DB_ENV->set_app_dispatch()</code> method configures operations performed
using the specified <a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a> handle, not all
operations performed on the underlying database environment.
</p>
<p>
The <code class="methodname">DB_ENV->set_app_dispatch()</code> method may not be called after the
<a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a> method is
called. If the database environment already exists when
<a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a> is called, the
information specified to <code class="methodname">DB_ENV->set_app_dispatch()</code> must be
consistent with the existing environment or corruption can occur.
</p>
<p>
The <code class="methodname">DB_ENV->set_app_dispatch()</code> method returns a non-zero error value
on failure and 0 on success.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1666877"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1666931"></a>tx_recover</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>tx_recover</strong></span> parameter is the
application's abort and recovery function. The function takes four
parameters:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">dbenv</code>
</p>
<p>
The <span class="bold"><strong>dbenv</strong></span> parameter is the enclosing
database environment handle.
</p>
</li>
<li>
<p>
<code class="literal">log_rec</code>
</p>
<p>
The <span class="bold"><strong>log_rec</strong></span> parameter is a log
record.
</p>
</li>
<li>
<p>
<code class="literal">lsn</code>
</p>
<p>
The <span class="bold"><strong>lsn</strong></span> parameter is a log sequence
number.
</p>
</li>
<li>
<p>
<code class="literal">op</code>
</p>
<p>
The <span class="bold"><strong>op</strong></span> parameter is one of the
following values:
</p>
<div class="itemizedlist">
<ul type="circle">
<li>
<p><a id="set_app_dispatch_DB_TXN_BACKWARD_ROLL"></a>
<code class="literal">DB_TXN_BACKWARD_ROLL</code>
</p>
<p>
The log is being read backward to determine which transactions have
been committed and to abort those operations that were not; undo the
operation described by the log record.
</p>
</li>
<li>
<p><a id="set_app_dispatch_DB_TXN_FORWARD_ROLL"></a>
<code class="literal">DB_TXN_FORWARD_ROLL</code>
</p>
<p>
The log is being played forward; redo the operation described by the
log record.
</p>
</li>
<li>
<p><a id="set_app_dispatch_DB_TXN_ABORT"></a>
<code class="literal">DB_TXN_ABORT</code>
</p>
<p>
The log is being read backward during a transaction abort; undo the
operation described by the log record.
</p>
</li>
<li>
<p><a id="set_app_dispatch_DB_TXN_APPLY"></a>
<code class="literal">DB_TXN_APPLY</code>
</p>
<p>
The log is being applied on a replica site; redo the operation
described by the log record.
</p>
</li>
<li>
<p><a id="set_app_dispatch_DB_TXN_PRINT"></a>
<code class="literal">DB_TXN_PRINT</code>
</p>
<p>
The log is being printed for debugging purposes; print the contents of
this log record in the desired format.
</p>
</li>
</ul>
</div>
<p>
The DB_TXN_FORWARD_ROLL and DB_TXN_APPLY operations frequently imply
the same actions, redoing changes that appear in the log record,
although if a recovery function is to be used on a replication client
where reads may be taking place concurrently with the processing of
incoming messages, DB_TXN_APPLY operations should also perform
appropriate locking. The macro DB_REDO(op) checks that the operation
is one of DB_TXN_FORWARD_ROLL or DB_TXN_APPLY, and should be used in
the recovery code to refer to the conditions under which operations
should be redone. Similarly, the macro DB_UNDO(op) checks if the
operation is one of DB_TXN_BACKWARD_ROLL or DB_TXN_ABORT.
</p>
</li>
</ul>
</div>
<p>
The function must return 0 on success and either <span class="bold"><strong>errno</strong></span>
or a value outside of the Berkeley DB error name space on failure.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1667211"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DB_ENV->set_app_dispatch()</code> <span>
<span>
method may fail and return one of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1667206"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
If the method was called after <a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a>
was called; or if an invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1667055"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a>, <a class="link" href="txn.html" title="Chapter 12. The DB_TXN Handle">DB_TXN</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1666928"></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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