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Oracle Database 10g Release 2 introduced the ability to have the server process
return control to the client without waiting for all the redo information to be written.
The plus side of this enhancement is that high-volume OLTP applications may
benefit from improved performance. The downside of this feature is that it opens a
How Oracle Handles Locking | 195
window of vulnerability??”the database could crash after a transaction had been committed,
but before the redo was written, which would make it impossible to recover
the committed transaction, so this feature should be used with caution.
A Conflicting Write Operation
The write operation previously described is a little different if there are two users,
Client A and Client B, who are trying to modify the same row of data at the same
time. The steps are as follows:
1. Client A modifies the employee name on the screen. Client A sends a SQL
UPDATE statement over the network to the server process.
2. The server process obtains an SCN for the statement and reads the data block
containing the target row.


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