#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.