# DbEnv.set_app_dispatch

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    import com.sleepycat.db.*;

    public interface DbTxnRecover
    {
        public abstract int
          tx_recover(DbEnv dbenv, Dbt log_rec, DbLsn lsn, int op);
    }
    public class DbEnv
    {
        public void set_app_dispatch(DbTxnRecover tx_recover)
    	throws DbException;
        ...
    }

# Description

Set the application's method to be called during transaction abort and recovery. This method must return 0 on success and either errno or a value outside of the Berkeley DB error name space on failure. It takes four arguments:

dbenv
  A Berkeley DB environment.

log_rec
  A log record.

lsn
  A log sequence number.

op
  One of the following values:

  Db.DB_TXN_BACKWARD_ROLL
    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.

  Db.DB_TXN_FORWARD_ROLL
    The log is being played forward; redo the operation described by the log record.

  Db.DB_TXN_ABORT
    The log is being read backward during a transaction abort; undo the operation described by the log record.

  Db.DB_TXN_APPLY
    The log is being applied on a replica site; redo the operation described by the log record.

  Db.DB_TXN_PRINT
    The log is being printed for debugging purposes; print the contents of this log record in the desired format.

The Db.DB_TXN_FORWARD_ROLL and Db.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.DB_TXN_APPLY operations should also perform appropriate locking. The macro DB_REDO(op) checks that the operation is one of Db.DB_TXN_FORWARD_ROLL or Db.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.DB_TXN_BACKWARD_ROLL or Db.DB_TXN_ABORT.

The DbEnv.set_app_dispatch method configures operations performed using the specified DbEnv handle, not all operations performed on the underlying database environment.

The DbEnv.set_app_dispatch interface may not be called after the DbEnv.open interface is called. If the database environment already exists when DbEnv.open 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 throws an exception that encapsulates a non-zero error value on failure.

# Errors

The DbEnv.set_app_dispatch method may fail and throw an exception encapsulating a non-zero error for the following conditions:

EINVAL
  An invalid flag value or parameter was specified.

  Called after DbEnv.open was called.

The DbEnv.set_app_dispatch method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the DbEnv.set_app_dispatch method may fail and throw a DbRunRecoveryException, in which case all subsequent Berkeley DB calls will fail in the same way.

# Class

DbEnv, DbTxn

# See Also

Transaction Subsystem and Related Methods`

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