Redo Log and Supplemental Logging related doubts

Question

Hi Friends,
I am studying Supplemental logging in detail. Have read lots of articles and oracle documentation about it and redo logs. But couldnot found answers of some doubts..
Please help me clear it.
Scenario: we have one table with primary key. And we execute an update query on that table which is not using the primary key column in any clause..
Question: In this case, does the redo log entry generated for the changes done by update query contain the primary columns values..?
Question: If we have any table with primary key, do we need to enable the supplemental logging on primary columns of that table? If yes, in which circumstances, do we need to enable it?
Question: If we have to configure stream replication on that table(having primary key), why do we actually need to enable its supplemental logging ( I have read the documentation saying that stream requires some more information so.., but actually what information does it need. Again this question is highly related to the first question.)
Also please suggest any good article/site which provide inside details of redo log and supplemental logging, if you know.
Regards,
Dipali..

Answer 1

1) Assuming you are not updating the primary key column and supplemental logging is not enabled, Oracle doesn't need to log the primary key column to the redo log, just the ROWID.
2) Is rather hard to answer without being tautological. You need to enable supplemental logging if and only if you have some downstream use for additional columns in the redo logs. Streams, and those technologies built on top of Streams, are the most common reason for enabling supplemental logging.
3) If you execute an update statement like
UPDATE some_table
  SET some_column = new_value
WHERE primary_key = some_key_value
   AND <<other conditions as well>>and look at an update statement that LogMiner builds from the redo logs in the absence of supplemental logging, it would basically be something like
UPDATE some_table
  SET some_column = new_value
WHERE rowid = rowid_of_the_row_you_updatedOracle doesn't need to replay the exact SQL statement you issued, (and thus it doesn't have to write the SQL statement to the redo log, it doesn't have to worry if the UPDATE takes a long time to run (otherwise, it would take as long to apply an archived log as it did to generate the log, which would be disasterous in a recovery situation), etc). It just needs to reconstruct the SQL statement from the information in redo, which is just the ROWID and the column(s) that changed.
If you try to run this statement on a different database (via Streams, for example) the ROWIDs on the destination database are likely totally different (since a ROWID is just a physical address of a row on disk). So adding supplemental logging tells Oracle to log the primary key column to redo and allows LogMiner/ Streams/ etc. to reconstruct the statement using the primary key values for the changed rows, which would be the same on both the source and destination databases.
Justin