org.xmlBlaster.contrib.dbwatcher.detector
Interface I_ChangeDetector

All Known Implementing Classes:

MD5ChangeDetector, TimestampChangeDetector

public interface I_ChangeDetector

This interface hides the plugin which checks if the data has changed.

There are many ways to detect DB changes, we provide a plugin for MD5 and timestamp checking

1. Changes are delivered by a MOM

   No DbWatcher is needed: This is the proper approach. As legacy systems have various channels which manipulate the DB directly it is no solution for older systems.

2. Modify/Creation timestamp column

   A trigger adds the timestamp to each table
   -> This changes the DB schema

3. Sequence of primary key

   Tables which contain a growing sequence of keys may use this to detect inserts
   -> Failes for 'update'

4. Using a LogMiner

   -> Is database specific and consumes a lot of CPU/memory

5. Audit tables (with trigger)

   Need to start database in audit mode -> How does it work in a portable way?

6. Having a trigger for each table

   The trigger notifies a stored procedure
   -> This needs to change the DB -> What if foreign database? http://www.oracle.com/technology/oramag/oracle/03-jan/o13java.html

7. Flashback queries

   -> What is this?

8. Use ora_rowscan (since Oracle 10g, similar for MS-SQLServer)

   Example for Oracle (http://www.remote-dba.net/10g_26.htm):
   select scn_to_timestamp(ora_rowscn) FROM A where ora_rowscn IS NOT null;
   Allows to retrieve the rowchange timestamps
   SQLServer uses the column type rowVersion.
   -> Missing for Oracle 9 and other DBs, Oracle 10g and MSQLServer support it.

9. Using a customized select with MD5

   Query everything and remember the last state with MD5. On change send the complete data again.

Author:

Marcel Ruff

Method Summary

int	checkAgain(java.util.Map attrMap) Check the observed data for changes.
void	init(I_Info info, I_ChangeListener changeListener, I_DataConverter dataConverter) Needs to be called after construction.
void	shutdown() Cleanup resources.

Method Detail

init

public void init(I_Info info,
                 I_ChangeListener changeListener,
                 I_DataConverter dataConverter)
          throws java.lang.Exception

Needs to be called after construction.

Parameters:

info - The configuration

changeListener - The listener to notify if something has changed

dataConverter - If not null the data will be transformed immediately during change detection

Throws:

java.lang.Exception

checkAgain

public int checkAgain(java.util.Map attrMap)
               throws java.lang.Exception

Check the observed data for changes.

Parameters:

attrMap - This map can be null. The event source can transport some specific information to help the changeDetector doing its work efficiently.

Returns:

> 0 if the observed data has changed. If supported by the plugin the the number of changed rows,

Throws:

java.lang.Exception - Can be of any type

shutdown

public void shutdown()
              throws java.lang.Exception

Cleanup resources.

Throws:

java.lang.Exception - Can be of any type