supplemental logging questions and golden gate
- From: Dba DBA <oracledbaquestions@xxxxxxxxx>
- To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 19 Jul 2011 10:48:01 -0400
We are going to use supplemental logging to work with Golden Gate. Golden
Gate is going to be used to stream data to other Oracle Databases and to
Teradata. I have some questions about supplemental loggings.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14215/logminer.htm#sthref2000
1. I believe the documentations says that during updates supplemental
logging adds redo for 2 things
-- primary or unique key (assuming we have a key and do not need to do
all records)
-- before image of the update
However, isn't the before image already captured? Whern you do an update,
the befoer image is copied to the undo tables space which is then written to
redo. This is necessary for rollback. I think this is saying that the before
image is needed after a commit is done, so that downstream Golden Gate can
tell which data to apply? I am not sure why. If you have the key and the
after image, isn't that enough? Or is this for some kind of rollback
downstream?
2. Inserts/Deletes: just adds the primary or unique key (assuming you have
one and do not add need to log all rows). I believe redo logs normally just
track the rowid right?
3. not having a key on a table wth alot of columns can significantly
increase redo generation. Since if you are updating 1 row, you need to write
every column to the redo logs so that downstream golden gate can do a diff
to apply the changes. Does this affect recovery at all other than you have
more redo. Or will the racle recovery mechanism ignore the supplemental
logging?
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