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<b>DB_ENV->set_app_dispatch</b>
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<b><pre>
#include <db.h>
<p>
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></b>
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<b>Description: DB_ENV->set_app_dispatch</b>
<p>Declare a function to be called during transaction abort and recovery
to process application-specific log records.</p>
<p>The DB_ENV->set_app_dispatch method configures operations performed using the specified
<a href="../api_c/env_class.html">DB_ENV</a> handle, not all operations performed on the underlying
database environment.</p>
<p>The DB_ENV->set_app_dispatch method may not be called after the <a href="../api_c/env_open.html">DB_ENV->open</a> method is
called.
If the database environment already exists when
<a href="../api_c/env_open.html">DB_ENV->open</a> is called, the information specified to DB_ENV->set_app_dispatch
must be consistent with the existing environment or corruption can
occur.</p>
<p>The DB_ENV->set_app_dispatch method
returns a non-zero error value on failure
and 0 on success.
</p>
<b>Parameters</b> <br>
<b>tx_recover</b><ul compact><li>The <b>tx_recover</b> parameter is the application's abort and recovery
function. The function takes four parameters:
<br>
<b><b>dbenv</b></b><ul compact><li>The <b>dbenv</b> parameter is the enclosing database environment handle.</ul>
<b><b>log_rec</b></b><ul compact><li>The <b>log_rec</b> parameter is a log record.</ul>
<b><b>lsn</b></b><ul compact><li>The <b>lsn</b> parameter is a log sequence number.</ul>
<b><b>op</b></b><ul compact><li>The <b>op</b> parameter is one of the following values:</ul>
<br>
<b><a name="DB_TXN_BACKWARD_ROLL">DB_TXN_BACKWARD_ROLL</a></b><ul compact><li>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.</ul>
<b><a name="DB_TXN_FORWARD_ROLL">DB_TXN_FORWARD_ROLL</a></b><ul compact><li>The log is being played forward; redo the operation described by the log
record.</ul>
<b><a name="DB_TXN_ABORT">DB_TXN_ABORT</a></b><ul compact><li>The log is being read backward during a transaction abort; undo the
operation described by the log record.</ul>
<b><a name="DB_TXN_APPLY">DB_TXN_APPLY</a></b><ul compact><li>The log is being applied on a replica site; redo the operation
described by the log record.</ul>
<b><a name="DB_TXN_PRINT">DB_TXN_PRINT</a></b><ul compact><li>The log is being printed for debugging purposes; print the contents of
this log record in the desired format.</ul>
<br>
<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>
<br>
<p>The function must return 0 on success and either <b>errno</b> or a
value outside of the Berkeley DB error name space on failure.</p></ul>
<br>
<br><b>Errors</b>
<p>The DB_ENV->set_app_dispatch method
may fail and return one of the following non-zero errors:</p>
<br>
<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_c/env_open.html">DB_ENV->open</a> was called; or if an
invalid flag value or parameter was specified.</ul>
<br>
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<br><b>Class</b>
<a href="../api_c/env_class.html">DB_ENV</a>, <a href="../api_c/txn_class.html">DB_TXN</a>
<br><b>See Also</b>
<a href="../api_c/txn_list.html">Transaction Subsystem and Related Methods</a>
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