Redo is written before the actual data is committed. This could be
microseconds, or it could be hours. Any recovery would be seriously
compromised if the redo was not written as soon as a single change was
made to the data.
As each insert/update/delete makes a change to a row, a redo vector
for that change (and only that change) is written to the log buffer.
Even if that insert/update/delete is immediately rolledback, the
original entry is still in the redo log. Also remember that a redo
entry is written for the change to the undo/rollback segment. In terms
of redo activity, an insert generates an insert redo entry and a redo
entry for the undo 'delete' entry. For a delete, there is a delete redo
entry and a redo entry for the undo 'insert' entry.
Received on Mon Aug 29 2005 - 15:52:14 CDT
