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DbEnv::set_app_dispatch
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#include &lt;db_cxx.h&gt;

int
DbEnv::set_app_dispatch(int (*tx_recover)(DbEnv *dbenv,
 Dbt *log_rec, DbLsn *lsn, db_recops op));
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Description: DbEnv::set_app_dispatch
Declare a function to be called during transaction abort and recovery
to process application-specific log records.
The DbEnv::set_app_dispatch method configures operations performed using the specified
<a href="../../db4-devel-4.7.25/api_cxx/env_class.html">DbEnv</a> handle, not all operations performed on the underlying
database environment.
The DbEnv::set_app_dispatch method may not be called after the <a href="../../db4-devel-4.7.25/api_cxx/env_open.html">DbEnv::open</a> method is
called.
If the database environment already exists when
<a href="../../db4-devel-4.7.25/api_cxx/env_open.html">DbEnv::open</a> is called, the information specified to DbEnv::set_app_dispatch
must be consistent with the existing environment or corruption can
occur.
The DbEnv::set_app_dispatch 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.

Parameters 
 tx_recover<ul compact><li>The tx_recover parameter is the application's abort and recovery
function. The function takes four parameters:
 
dbenv<ul compact><li>The dbenv parameter is the enclosing database environment handle.</ul>
log_rec<ul compact><li>The log_rec parameter is a log record.</ul>
lsn<ul compact><li>The lsn parameter is a log sequence number.</ul>
op<ul compact><li>The op parameter is one of the following values:</ul>
 
<a name="DB_TXN_BACKWARD_ROLL">DB_TXN_BACKWARD_ROLL</a><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>
<a name="DB_TXN_FORWARD_ROLL">DB_TXN_FORWARD_ROLL</a><ul compact><li>The log is being played forward; redo the operation described by the log
record.</ul>
<a name="DB_TXN_ABORT">DB_TXN_ABORT</a><ul compact><li>The log is being read backward during a transaction abort; undo the
operation described by the log record.</ul>
<a name="DB_TXN_APPLY">DB_TXN_APPLY</a><ul compact><li>The log is being applied on a replica site; redo the operation
described by the log record.</ul>
<a name="DB_TXN_PRINT">DB_TXN_PRINT</a><ul compact><li>The log is being printed for debugging purposes; print the contents of
this log record in the desired format.</ul>
 
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.
 
The function must return 0 on success and either errno or a
value outside of the Berkeley DB error name space on failure.</ul>
 
 Errors
The DbEnv::set_app_dispatch method
may fail and throw
<a href="../../db4-devel-4.7.25/api_cxx/except_class.html">DbException</a>,
encapsulating one of the following non-zero errors, or return one of
the following non-zero errors:
 
EINVAL<ul compact><li>If the method was called after <a href="../../db4-devel-4.7.25/api_cxx/env_open.html">DbEnv::open</a> was called; or if an
invalid flag value or parameter was specified.</ul>
 
<hr size=1 noshade>
 Class
<a href="../../db4-devel-4.7.25/api_cxx/env_class.html">DbEnv</a>, <a href="../../db4-devel-4.7.25/api_cxx/txn_class.html">DbTxn</a>
 See Also
<a href="../../db4-devel-4.7.25/api_cxx/txn_list.html">Transaction Subsystem and Related Methods</a>
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