#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));
Declare a function to be called during transaction abort and recovery to process application-specific log records.
The DB_ENV->set_app_dispatch() method configures operations performed
using the specified DB_ENV handle, not all
operations performed on the underlying database environment.
The DB_ENV->set_app_dispatch() method may not be called after the
DB_ENV->open() method is
called. If the database environment already exists when
DB_ENV->open() is called, the
information specified to DB_ENV->set_app_dispatch() must be
consistent with the existing environment or corruption can occur.
The DB_ENV->set_app_dispatch() method returns a non-zero error value
on failure and 0 on success.
The tx_recover parameter is the application's abort and recovery function. The function takes four parameters:
dbenv
The dbenv parameter is the enclosing database environment handle.
log_rec
The log_rec parameter is a log record.
lsn
The lsn parameter is a log sequence number.
op
The op parameter is one of the following values:
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.
The log is being played forward; redo the operation described by the log record.
The log is being read backward during a transaction abort; undo the operation described by the log record.
The log is being applied on a replica site; redo the operation described by the log record.
The log is being printed for debugging purposes; print the contents of this log record in the desired format.
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.
The DB_ENV->set_app_dispatch()
method may fail and return one of the following non-zero errors:
If the method was called after DB_ENV->open() was called; or if an invalid flag value or parameter was specified.