Supplemental Logging

When Supplemental Logging is enabled, either some selected columns or all columns are specified for extra logging. They are called a supplemental log group and consist of nothing but a set of additional columns that are being logged. There are two types of supplemental log groups that determine when columns in the log group are logged:

• Unconditional Supplemental Log Groups - The before-images of specified columns are logged any time a row is updated, regardless of whether the update affected any of the specified columns. This can be referred to as an ALWAYS log group.
   

• Conditional Supplemental Log Groups - The before-images of all specified columns are logged only if at least one of the columns in the log group is updated.

Supplemental Logging can be enabled at database level or at the table level. When it is enabled at database level, there are two types:

• Minimal Logging
   

• Identification Key Logging

Database Level Logging

With the minimal database level supplemental logging, the database logs the minimal amount of information needed for LogMiner or for the Streams Capture process to identify, group, and merge the redo operations associated with DML changes.

To enable minimal supplemental logging, the following statement can be executed:

SQL> ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;