Interface Loggable

    • Field Detail

      • FIRST

        static final int FIRST
        Each loggable belongs to one or more groups of similar functionality. Grouping is a way to quickly sort out log records that are interesting to different modules or different implementations. When a module makes loggable and sent it to the log file, it must mark this loggable with one or more of the following group. If none fit, or if the loggable encompasses functionality that is not described in existing groups, then a new group should be introduced. Grouping has no effect on how the record is logged or how it is treated in rollback or recovery. The following groups are defined. This list serves as the registry of all loggable groups.
        See Also:
        Constant Field Values
    • Method Detail

      • doMe

        void doMe​(Transaction xact,
                  LogInstant instant,
                  LimitObjectInput in)
           throws StandardException,
                  java.io.IOException
        Apply the change indicated by this operation and optional data. If this method fail, the system will be shut down because the log record has already been written to disk. Moreover, the log record will be replayed during recovery and this doMe method will be called on the same page again, so if it fails again, recovery will fail and the database cannot be started. So it is very important to make sure that every resource you need, such as disk space, has been acquired before the logAndDo method is called!
        This method cannot acquire any resource (like latching of a page) since it is called underneath the logging system, ie., the log record has already been written to the log stream.

        The available() method of in indicates how much data can be read, i.e. how much was originally written.

        Parameters:
        xact - the Transaction
        instant - the log instant of this operation
        in - optional data
        Throws:
        java.io.IOException - Can be thrown by any of the methods of in.
        StandardException - Standard Derby policy.
      • getPreparedLog

        ByteArray getPreparedLog()
                          throws StandardException
        The log operations are responsible to create the ByteArray, and the log operations should write out any optional data for the change to the ByteArray. The ByteArray can be prepared when the log operation is constructed, or it can be prepared when getPreparedLog() is called. Called by the log manager to allow the log operation to pass the buffer which contains optional data that will be available in to doMe() methods.
        Throws:
        StandardException - Standard Derby policy.
      • needsRedo

        boolean needsRedo​(Transaction xact)
                   throws StandardException
        Determine if the operation should be reapplied in recovery redo. If redo is needed, acquire any resource that is necessary for the loggable's doMe method. These need to be released in the releaseResource method.

        The sequence of events in recovery redo of a Loggable operation is:

      • Get the loggable operation. If loggable.needsRedo is false, then no need to redo this operation.
      • If loggable.needsRedo is true, all the resources necessary for applying the doMe is acquired in needsRedo.
      • If the loggable is actually a compensation operation, then the logging system will find the undoable operation that needs to be undone, call compensation.setUndoOp with the undoable operation.
      • The recovery system then calls loggable.doMe, which re-applies the loggable operation, or re-applies the compensation operation
      • The recovery system then calls loggable.releaseResource.
Parameters:
xact - The transaction trying to redo this operation
Returns:
true if operation needs redoing, false if not.
Throws:
StandardException - Standard Derby policy.
See Also:
releaseResource(org.apache.derby.iapi.store.raw.Transaction)