supplemental logging in oracle streams


i have a small question on supplemental logging in oracle streams. i am trying to configure oracle streams. in oracle documentation i have seen enable supplemental logging at table on source database. i did not quite understand what is supplemental logging. can any one clarify me.

in the documentation have seen this info.

supplemental logging

Additional column data placed in a redo log whenever an operation is performed. A capture process captures this additional information and places it in LCRs, and the additional information might be needed for an apply process to apply LCRs properly at a destination database.

what type additional data is placed when we enable supplemental logging.
what happen if i do not enable supplemental logging.

one more question is, i am configuring 1 way replication. do i need to enable archive log mode fro source database and target database?
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The Capture process captures this additional information and places it in LCRs.
Supplemental Logging is always configured at a source database, regardless of location of the Capture process that captures the changes that occur in the source database. Even if the capture process is configured at the downstream database, the source database needs to specify the Supplemental Logging. In the case of Streams replication, the Apply process uses the additional information in the LCRs to properly apply DML changes and DDL changes that are replicated from a source database to a destination database.

There are two types of supplemental log groups: Unconditional Supplemental Log Groups and Conditional Supplemental Log Groups.

Unconditional Supplemental Log Groups - The before images of specified columns are logged any time a row is updated, regardless of whether or not 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 table level.
Supplemental logging is additional data stored in the redo log that allows the target databases to determine which rows to update. It is a requirement of Streams and LogMiner.

In order to get Streams to work, you will need archiving enabled on your source database, as the streams capture process uses LogMiner, but it isnt absolutely necessary on the target. It is however good practice, and highly recommended.
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