Use Oracle Logminer to Analyse Logfile

We know that any changes to database is recored in online redo logfiles. If your database archival mode on then online redo log files are archived which contains the database changes. With these logfile we can analysis any changes in database.

In simple we can say an undo entry provides the values of data stored before a change and the redo entry provides the values of data stored after a change. Because undo segments are database changes, they also generate redo entries. So we can get them from online redo logs and then to archived logs.

So from online redo logs and from archived redo logs we can get database redo and undo information. But online and archived logs have an unpublished format and are not human-readable. With the DBMS_LOGMNR package we can analysis redo log files and can get back undo and redo information in a human readable format.

Another scenario of use of logminer is to investigate database past in time. With Flashback Query we can get prior values of the record in the table at some point in the past but is limited to UNDO_RETENTION parameter (which is often as short as 30 minutes for an OLTP database.).So in order to analysis past activity on the database logminer is a good choice.